Free World Trust v. Electro Santé Inc. et al.

citation(s): (2000) 2 S.C.R. 1024; neutral cite: 2000 S.C.C. 66; online;  (2001) 9 C.P.R. (4th) 168 (S.C.C. per Binnie J.)

JurisDictioncom.gif (2187 bytes)  Case Comment        © 2004 Donald M. Cameron





[1, p. 173]    The principal question that arises on this appeal is the extent to which a patent monopoly protects "the substance" or "the spirit" of an invention, as distinguished from what is literally described in the written claims, and whether on the facts of this case the claims patented by the appellant are sufficiently elastic to catch the electro-magnetotherapy machine of the respondent Électro Santé Inc.

[3, p. 173]    The appeal thus raises important questions about the scope and ambit of a patent owner's monopoly. Too much elasticity in the interpretation of the scope of the claims creates uncertainty and stifles competition. Too little protection robs inventors of the benefit they were promised in exchange for making a full and complete disclosure of the fruits of their ingenuity. The Quebec Court of Appeal held that the respondents' machines took neither the letter nor the substance of the appellant's patents. I think this conclusion was correct, although I get there by a somewhat different route. The appeal must therefore be dismissed.

[14, p. 178]    Patent claims are frequently analogized to "fences" and "boundaries", giving the "fields" of the monopoly a comfortable pretence of bright line demarcation. Thus, in Minerals Separation North American Corp. v. Noranda Mines, Ltd., [1947] Ex. C.R. 306, Thorson P. put the matter as follows, at p. 352:

By his claims the inventor puts fences around the fields of his monopoly and warns the public against trespassing on his property. His fences must be clearly placed in order to give the necessary warning and he must not fence in any property that is not his own. The terms of a claim must be free from avoidable ambiguity or obscurity and must not be flexible; they must be clear and precise so that the public will be able to know not only where it must not trespass but also where it may safely go.

[15, p. 178-179]    In reality, the "fences" often consist of complex layers of definitions of different elements (or "components" or "features" or "integers") of differing complexity, substitutability and ingenuity. A matrix of descriptive words and phrases defines the monopoly, warns the public and ensnares the infringer. In some instances, the precise elements of the "fence" may be crucial or "essential" to the working of the invention as claimed; in others the inventor may contemplate, and the reader skilled in the art appreciate, that variants could easily be used or substituted without making any material difference to the working of the invention. The interpretative task of the court in claims construction is to separate the one from the other, to distinguish the essential from the inessential, and to give to the "field" framed by the former the legal protection to which the holder of a valid patent is entitled.

[20, p. 180]    Based on the expert evidence given at trial as to the meaning of the terms used, and the understanding that these terms would convey at the date of the patent to an ordinary worker skilled in the art of electro-magnetotherapy devices and possessing the common knowledge of people engaged in that field, it appears that while some of the elements of the '156 and '361 patents are essential if the devices are to work as contemplated and claimed by the inventor, others are non-essential. The non-essential elements may be substituted or omitted without having a material effect on either the structure or the operation of the invention described in the claims.

[25] Anticipation by publication is a difficult defence to establish because courts recognize that it is all too easy after an invention has been disclosed to find its antecedents in bits and pieces of earlier learning. It takes little ingenuity to assemble a dossier of prior art with the benefit of 20-20 hindsight. In this case, the respondents contended that all of the essential elements of the appellant's alleged inventions were disclosed in a single publication, the Solov'eva article, which predated the patent application by almost 4 years. If this is correct, the patent would be invalid.

[26] The Solov'eva article was drawn to the respondents' attention by the appellant who cited it as prior art in the specification of the '361 patent itself.  The legal question is whether the Solov'eva article contains sufficient information to enable a person of ordinary skill and knowledge in the field to understand, without access to the two patents, “the nature of the invention and carry it into practical use without the aid of inventive genius but purely by mechanical skill” (H. G. Fox, The Canadian Law and Practice Relating to Letters Patent for Inventions (4th ed. 1969), at pp. 126-27).  In other words, was the information given by Solov'eva “for [the] purpose of practical utility, equal to that given in the patents in suit”? (Consolboard Inc. v. MacMillan Bloedel (Sask.) Ltd., [1981] 1 S.C.R. 504, per Dickson J. at p. 534), or as was memorably put in General Tire & Rubber Co. v. Firestone Tyre & Rubber Co., [1972] R.P.C. 457 (Eng. C.A.), at p. 486:

A signpost, however clear, upon the road to the patentee's invention will not suffice. The prior inventor must be clearly shown to have planted his flag at the precise destination before the patentee. 

The test for anticipation is difficult to meet:

One must, in effect, be able to look at a prior, single publication and find in it all the information which, for practical purposes, is needed to produce the claimed invention without the exercise of any inventive skill. The prior publication must contain so clear a direction that a skilled person reading and following it would in every case and without possibility of error be led to the claimed invention. (Beloit Canada Ltd. v. Valmet OY (1986), 8 C.P.R. (3d) 289 (F.C.A.), per Hugessen J.A., at p. 297)

[28, p. 183] The appeal in this Court was essentially directed to the infringement issues. It has been established, at least since Grip Printing and Publishing Co. of Toronto v. Butterfield (1885), 11 S.C.R. 291, that a patent owner has a remedy against an alleged infringer who does not take the letter of the invention but nevertheless appropriates its substance (or "pith and marrow"). This extended protection of the patentee is recognized in Anglo-Canadian law, and also finds expression in modified form in the United States under the doctrine of equivalents, which is said to be available against the producer of a device that performs substantially the same function in substantially the same way to obtain substantially the same result: Graver Tank & Mfg. Co. v. Linde Air Products Co., 339 U.S. 605 (1950), at p. 608.

[29, p. 183]    It is obviously an important public policy to control the scope of "substantive infringement". A purely literal application of the text of the claims would allow a person skilled in the art to make minor and inconsequential variations in the device and thereby to appropriate the substance of the invention with a copycat device while staying just outside the monopoly. A broader interpretation, on the other hand, risks conferring on the patentee the benefit of inventions that he had not in fact made but which could be deemed with hindsight to be "equivalent" to what in fact was invented. This would be unfair to the public and unfair to competitors. It is important that the patent system be fair as well as predictable in its operation.

[31, pp. 183-184]    The appeal thus raises the fundamental issue of how best to resolve the tension between "literal infringement" and "substantive infringement" to achieve a fair and predictable result. There has been considerable discussion of this issue in Canada and elsewhere, which I will discuss briefly in support of the following propositions:

(a)    The Patent Act promotes adherence to the language of the claims.

(b)    Adherence to the language of the claims in turn promotes both fairness and predictability.

(c)    The claim language must, however, be read in an informed and purposive way.

(d)    The language of the claims thus construed defines the monopoly. There is no recourse to such vague notions as the "spirit of the invention" to expand it further.

(e)    The claims language will, on a purposive construction, show that some elements of the claimed invention are essential while others are non-essential. The identification of elements as essential or non-essential is made:

(i)    on the basis of the common knowledge of the worker skilled in the art to which the patent relates;

(ii)    as of the date the patent is published;

(iii)    having regard to whether or not it was obvious to the skilled reader at the time the patent was published that a variant of a particular element would not make a difference to the way in which the invention works; or

(iv)    according to the intent of the inventor, expressed or inferred from the claims, that a particular element is essential irrespective of its practical effect;

(v)    without, however, resort to extrinsic evidence of the inventor's intention.

(f)    There is no infringement if an essential element is different or omitted. There may still be infringement, however, if non-essential elements are substituted or omitted.

[32, pp. 184-185]    Based on the foregoing principles, I conclude that the appellant's arguments must be rejected. As stated, the ingenuity of the patent lies not in the identification of a desirable result but in teaching one particular means to achieve it. The claims cannot be stretched to allow the patentee to monopolize anything that achieves the desirable result. It is not legitimate, for example, to obtain a patent for a particular method that grows hair on bald men and thereafter claim that anything that grows hair on bald men infringes. I turn then to the first of the propositions listed above.

[33, p. 185]    The Patent Act requires the letters patent granting a patent monopoly to include a specification which sets out a correct and full "disclosure" of the invention, i.e., "correctly and fully describe[s] the invention and its operation or use as contemplated by the inventor" (s. 34(1)(a)). The disclosure is followed by "a claim or claims stating distinctly and in explicit terms the things or combinations that the applicant regards as new and in which he claims an exclusive property or privilege" (s. 34(2)). It is the invention thus claimed to which the patentee receives the "exclusive right, privilege and liberty" of exploitation (s. 44). These provisions, and similar provisions in other jurisdictions, have given rise to two schools of thought. One school holds that the claim embodies a technical idea and claims construction ought to look to substance rather than form to protect the inventive idea underlying the claim language. This is sometimes called the "central claim drafting principle" and is associated with the German and Japanese patent systems: T. Takenaka, "Doctrine of Equivalents after Hilton Davis: A Comparative Law Analysis" (1996), 22 Rutgers Computer & Tech. L. J. 479, at pp. 491, 502 and 519. The other school of thought supporting what is sometimes called the "peripheral claiming principle" emphasizes the language of the claims as defining not the underlying technical idea but the legal boundary of the state-conferred monopoly. Traditionally, for reasons of fairness and predictability, Canadian courts have preferred the latter approach.

[34, p. 185]    The "spirit of the invention" school in this country relies on Electrolier Manufacturing Co. v. Dominion Manufacturers Ltd., [1934] S.C.R. 436. In that case, which involved a method to pivot handles for coffins, Rinfret J. spoke of "the spirit of the invention" but did so in a direct quote from the patent itself, at p. 443:

What the appellant did -- and in that his infringement truly consists -- was to take the idea which formed the real subject-matter of the invention. It does not matter whether he also adopted the substitution of the two holes for the bar in the pivoting means. The precise form of these means was immaterial. In the language of the patent, they could be changed "without departing from the spirit of the invention". [Emphasis added.]

Rinfret J. went on at p. 444 to tie explicitly his finding of infringement to a "fair interpretation of the language of the specification".

[35, p. 186]    The debate between the advocates of the "central claiming principle" and advocates of the "peripheral claiming principle" can each find precedents to support them. As long ago as Smith Incubator Co. v. Seiling, [1936] S.C.R. 251, at p. 259, counsel pointed out that there appeared to be these two mutually inconsistent lines of authority:

According to one of these it is proper to consider what is "the pith and substance" or the "spirit" of the invention and to give effect to the patent accordingly. The other is to regard the claims as definitely determining the scope of the monopoly which the patent purports to grant and to give or refuse them effect according to the expressions they contain when these expressions are properly construed and their meaning determined.

To which Rinfret J., for the Court, responded at pp. 259-60:

In our view, the rule is that the claims must be regarded as definitely determining the scope of the monopoly, having regard to the due and proper construction of the expressions they contain.

[40, p. 188]    The judgment of Lord Diplock was considered and applied by our Federal Court of Appeal in Eli Lilly & Co. v. O'Hara Manufacturing Ltd. (1989), 26 C.P.R. (3d) 1, and its progeny. The primacy of the claims language was already rooted deeply in our jurisprudence and should, I think, be affirmed again on this appeal.

(b)    Adherence to the Language of the Claims in Turn Promotes both Fairness and Predictability

[41, p. 188]    The scope of patent protection must not only be fair, it must be reasonably predictable. A patent is, after all, a public instrument issued under statutory authority which may result in severe financial consequences for its infringement. The scope of its prohibition should be made clear so that members of the public may know where they can go with impunity. As was said in another public law connection by Gonthier J. in R. v. Nova Scotia Pharmaceutical Society, [1992] 2 S.C.R. 606, at p. 639, precision in public enactments is required to "sufficiently delineate an area of risk".

[42, p. 188-189]     The patent system is designed to advance research and development and to encourage broader economic activity. Achievement of these objectives is undermined however if competitors fear to tread in the vicinity of the patent because its scope lacks a reasonable measure of precision and certainty. A patent of uncertain scope becomes "a public nuisance" (R.C.A. Photophone, Ld. v. Gaumont-British Picture Corp. (1936), 53 R.P.C. 167 (Eng. C.A.), at p. 195). Potential competitors are deterred from working in areas that are not in fact covered by the patent even though costly and protracted litigation (which in the case of patent disputes can be very costly and protracted indeed) might confirm that what the competitors propose to do is entirely lawful. Potential investment is lost or otherwise directed. Competition is "chilled". The patent owner is getting more of a monopoly than the public bargained for. There is a high economic cost attached to uncertainty and it is the proper policy of patent law to keep it to a minimum.

[43, p. 189]    The patent owner, competitors, potential infringers and the public generally are thus entitled to clear and definite rules as to the extent of the monopoly conferred. This in turn requires that the subjective or discretionary element of claims interpretation (e.g., the elusive quest for "the spirit of the invention") be kept to the minimum, consistent with giving "the inventor protection for that which he has actually in good faith invented" (Western Electric Co. v. Baldwin International Radio of Canada, [1934] S.C.R. 570, at p. 574). Predictability is achieved by tying the patentee to its claims; fairness is achieved by interpreting those claims in an informed and purposive way.

(c)    The Claims Must Be Construed in an Informed and Purposive Way

[44, p. 189]    The courts have traditionally protected a patentee from the effects of excessive literalism. The patent is not addressed to an ordinary member of the public, but to a worker skilled in the art described by Dr. Fox as

a hypothetical person possessing the ordinary skill and knowledge of the particular art to which the invention relates, and a mind willing to understand a specification that is addressed to him. This hypothetical person has sometimes been equated with the "reasonable man" used as a standard in negligence cases. He is assumed to be a man who is going to try to achieve success and not one who is looking for difficulties or seeking failure.  (Fox, supra, at p. 184)

It is the "common knowledge" shared by competent "ordinary workers" that is brought to bear on the interpretation: Fox, supra, at p. 204; Terrell on the Law of Patents (15th ed. 2000), at p. 125; I. Goldsmith, Patents of Invention (1981), at p. 116. The present appeal does not raise great subtleties of interpretation. The experts called by the parties here more or less agreed on the significance of what is stated in the claims. The electro-magnetotherapy is to be controlled by "circuit means". The present appeal turns on the scope of the legal protection that arises out of that fact.

(d)    The Language of the Claims Thus Construed Defines the Monopoly. There Is no Recourse to such Vague Notions as "Spirit of the Invention" to Expand it Further

[45, p. 190]    There appears to be a continuing controversy in some quarters as to whether there are two approaches to infringement (literal and substantive) or only one approach, namely infringement of the claims as written but "purposively" construed.

[46, p. 190]    In the two-step approach, the court construes the claims and determines whether the device accused of infringement has literally taken the invention. If not, the court proceeds to the second step of asking itself whether "in substance" the invention was wrongfully appropriated. On occasion, treatment of the second step in specific cases has attracted criticism as being subjective and unduly discretionary. Once the inquiry is no longer anchored in the language of the claims, the court may be heading into unknown waters without a chart. The one-step approach has to build flexibility and common sense into the initial claims construction because there is no second step.

[47, p. 190]    The "single cause of action" approach was advocated by Lord Diplock in Catnic, supra, at p. 242:

My Lords, in their closely reasoned written cases in this House and in the oral argument, both parties to this appeal have tended to treat "textual infringement" and infringement of the "pith and marrow" of an invention as if they were separate causes of action, the existence of the former to be determined as a matter of construction only and of the latter upon some broader principle of colourable evasion. There is, in my view, no such dichotomy; there is but a single cause of action and to treat it otherwise, particularly in cases like that which is the subject of the instant appeal, is liable to lead to confusion.

[50, p. 191]    I do not suggest that the two-stage approach necessarily ends at a different destination than the one-stage approach, or that the two-stage approach has resulted in abuse. I think we should now recognize, however, that the greater the level of discretion left to courts to peer below the language of the claims in a search for "the spirit of the invention", the less the claims can perform their public notice function, and the greater the resulting level of unwelcome uncertainty and unpredictability. "Purposive construction" does away with the first step of purely literal interpretation but disciplines the scope of "substantive" claims construction in the interest of fairness to both the patentee and the public. In my view its endorsement by the Federal Court of Appeal in O'Hara was correct.

(e)    The Claims Language Will, on a Purposive Construction, Show that Some Elements of the Claimed Invention Are Essential While Others Are Non-essential. This Allocation Will Be Made in the Following Manner:

(i)    On the Basis of the Common Knowledge of the Worker Skilled in the Art to which the Patent Relates

[51, p. 191]    This point is addressed more particularly in Whirlpool Corp. v. Camco Inc., [2000] 2 S.C.R. 1067, 2000 SCC 67 and Whirlpool Corp. v. Maytag Corp., [2000] 2 S.C.R. 1116, 2000 SCC 68, released concurrently. The involvement in claims construction of the skilled addressee holds out to the patentee the comfort that the claims will be read in light of the knowledge provided to the court by expert evidence on the technical meaning of the terms and concepts used in the claims. The words chosen by the inventor will be read in the sense the inventor is presumed to have intended, and in a way that is sympathetic to accomplishment of the inventor's purpose expressed or implicit in the text of the claims. However, if the inventor has misspoken or otherwise created an unnecessary or troublesome limitation in the claims, it is a self-inflicted wound. The public is entitled to rely on the words used provided the words used are interpreted fairly and knowledgeably.

(ii)    What Constitutes an "Essential" Element Is to Be Interpreted in Light of the Knowledge of the Art at the Date of the Publication of the Patent Specification

[52, p. 192]    The substitutability of non-essential elements derives from an informed interpretation of the language of the claims at the time they are revealed to the target audience of persons skilled in the relevant art. Thus Dickson J., in Consolboard, supra, spoke at p. 523 of "what a competent workman reading the specification at its date would have understood it to have disclosed and claimed" (emphasis added). See also Fox, supra, at p. 204. The date of publication was identified by Lord Diplock in Catnic, supra, and picked up by Hoffmann J. (as he then was) in Improver Corp. v. Remington Consumer Products Ltd., [1990] F.S.R. 181 (Pat. Ct.), at p. 182:

Would this (i.e.: that the variant had no material effect) have been obvious at the date of publication of the patent to a reader skilled in the art? If no, the variant is outside the claim. [Emphasis added.]

[54, p. 193]    There remains, however, a choice between the date of issuance of the patent and the date of its publication because under the former Act the date of issue and the date of publication were the same. Now, as a result of the obligations assumed by Canada under the 1970 Patent Cooperation Treaty implemented by s. 10 of the new Act (S.C. 1993, c. 15, s. 28), the patent specification is "laid open" 18 months after the effective date of the Canadian patent application. In my view, the same logic that favoured the date of issuance/publication as the critical date for claims construction under the former Act, favours the choice of the "laid open" date under the new Act. On that date, the invention is disclosed to the public, those interested have some ability to oppose the grant of the patent applied for, and the applicant for the patent is eventually allowed to claim reasonable compensation (s. 55(2)), provided the patent is ultimately granted, from and after the "laid open" date. The public, the patentee, its competitors and potential infringers all have an interest and/or concern from that date forward. The notional skilled addressee has a text available for interpretation. In summary, public disclosure and the triggering of legal consequences on the "laid open" date, as well as the policy considerations that underpinned the earlier case law, favour that date over the other possibilities as the critical date for the purpose of claims construction.

(iii)    Regard Is to Be Had to Whether It Was Obvious at the Time the Patent Was Published that Substitution of a Different Variant Would Make a Difference to the Way in Which the Invention Works

[55, p. 193-194]    It would be unfair to allow a patent monopoly to be breached with impunity by a copycat device that simply switched bells and whistles, to escape the literal claims of the patent. Thus the elements of the invention are identified as either essential elements (where substitution of another element or omission takes the device outside the monopoly), or non-essential elements (where substitution or omission is not necessarily fatal to an allegation of infringement). For an element to be considered non-essential and thus substitutable, it must be shown either (i) that on a purposive construction of the words of the claim it was clearly not intended to be essential, or (ii)
that at the date of publication of the patent, the skilled addressees would have appreciated that a particular element could be substituted without affecting the working of the invention, i.e., had the skilled worker at that time been told of both the element specified in the claim and the variant and "asked whether the variant would obviously work in the same way", the answer would be yes: Improver Corp. v. Remington, supra, at p. 192. In this context, I think "work in the same way" should be taken for our purposes as meaning that the variant (or component) would perform substantially the same function in substantially the same way to obtain substantially the same result. In Improver Corp. v. Remington, Hoffmann J. attempted to reduce the essence of the Catnic analysis to a series of concise questions, at p. 182:

(i) Does the variant have a material effect upon the way the invention works? If yes, the variant is outside the claim. If no: --

(ii) Would this (i.e.: that the variant had no material effect) have been obvious at the date of publication of the patent to a reader skilled in the art? If no, the variant is outside the claim. If yes: --

(iii) Would the reader skilled in the art nevertheless have understood from the language of the claim that the patentee intended that strict compliance with the primary meaning was an essential requirement of the invention? If yes, the variant is outside the claim.

[56, p. 194]    The three questions are not exhaustive but they encapsulate the heart of Lord Diplock's analysis, and have been endorsed in subsequent English cases.

[57, p. 194]    In AT & T Technologies, supra, at p. 257, Reed J. derived a series of interpretive principles from Catnic, supra, O'Hara, supra, and other cases. Her third principle is as follows:

(3) if a variant of an aspect of a claim has no material effect on the way the invention works there is a presumption that the patent is infringed and that the patentee intended that that variant falls within the scope of the claim. . . . [Emphasis added.]

The desirability of such a presumption is supported by some commentators (see, e.g., J.-C. Boudreau, "AT&T Technologies: A Contribution to the Purposive Construction Approach for Patent Infringement Analysis in Canada" (1998-99), 15 C.I.P.R. 323).  If this proposition is taken to mean that a presumption of non-essentiality will arise if it is established in light of the knowledge of substitutability existing at the date of the infringement (AT & T Technologies, supra, at p. 262) that a variant would have no material effect on the way the invention works then, with respect, I disagree with it.  The effect would be that the ambit of the monopoly would grow over the life of the patent as new substitutes are developed and absorbed into the common knowledge of the skilled worker.  The inventor cannot be thought to have the necessary "intent" in relation to after-created knowledge except in the irrelevant sense of intending to reap the benefit of the maximum coverage available. In my view, Catnic, supra, and O'Hara, supra, were correct to put the onus on the patentee to establish known and obvious substitutability at the date of publication of the patent.  If the patentee fails to discharge that onus, the descriptive word or expression in the claim is to be considered essential unless the context of the claims language otherwise dictates.

[60, p. 196]    The facts of O'Hara have an echo in the facts of this case. Claim 1 of the '156 patent stipulates the "said magnetization coil being stationary" during treatment. Whether the magnetization coil is stationary may or may not affect the way the device works, but the inventor has explicitly so stipulated.

[66, p. 197-198]    In my view, those references to the inventor's intention refer to an objective manifestation of that intent in the patent claims, as interpreted by the person skilled in the art, and do not contemplate extrinsic evidence such as statements or admissions made in the course of patent prosecution. To allow such extrinsic evidence for the purpose of defining the monopoly would undermine the public notice function of the claims, and increase uncertainty as well as fuelling the already overheated engines of patent litigation. The current emphasis on purposive construction, which keeps the focus on the language of the claims, seems also to be inconsistent with opening the pandora's box of file wrapper estoppel. If significant representations are made to the Patent Office touching the scope of the claims, the Patent Office should insist where necessary on an amendment to the claims to reflect the representation.

[68, p. 198]    While the foregoing principles will have to be adapted to the exigencies of different types of patents, it may be helpful to summarize how they apply in this case.

(1)At the claims construction stage, the wording of the claims was analysed to isolate the descriptive words and phrases which identify the elements of the invention. There is no need here to make heavy weather in the details. The claims specify the presence of "circuit means" to control the electro-magnetotherapy. There is nothing in the context of the claims to suggest that the inventor considered circuit means to be non-essential. On the contrary, it is the core of the invention. Equally, there was no evidence that at the date of publication of the patent the ordinary skilled worker would have appreciated that there were variants that could perform substantially the same function in substantially the same way to achieve substantially the same result as the circuit means specified in the patent.

(2)Control of the magnetotherapy by circuit means was therefore an essential element of the invention.

(3)At the infringement analysis stage, the accused Électro-Santé device is now to be examined and its constituent elements similarly identified.

(4)If the accused device takes all of the essential elements of the invention, there is infringement.

[73, p. 199]    The claims clearly require "circuit means". As mentioned, a skilled reader in 1981 or 1983 would associate that descriptive phrase with specific technology and consider the use of such technology essential to the claimed invention. The fact that the Électro-Santé device uses a microcontroller to perform a similar or even the same function does not bring it within the claim. It performs the function in a very different way. Moreover, there is no reason to think the inventor didn't mean what he said, or considered the use of "circuit means" a non-essential element of the claims, or intended to claim more broadly than "circuit means" and thereby put at risk for "covetous claiming" the validity of the patents. As the Court of Appeal observed, the means of control of amplitude and frequency is precisely the difference that validated the patents over the prior art embodied in such predecessor magnetotherapy machines as the Magnétopace, Myodynamic and Elec devices.

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