May And Baker Ltd & Ors v. Boots Pure Drug Company Ltd

Under section 22 of the Patents and Designs Acts 1907 to 1946, the inventions claimed by the original and amended specifications must be compared by construing each specification as a whole. The comparison concerns the inventions, not merely the areas of monopoly defined by the claims.

An amendment is prohibited where it replaces a generic invention, founded upon an asserted property common to a class, with specific inventions founded upon the empirically established properties of selected members. The specific products may have been fully described as examples in the original specification. That fact does not prevent the amendment from claiming a substantially different invention when the products possess their value through characteristics peculiar to them.

The appellants held a patent concerning benzene-sulphonamido-thiazole derivatives. The original specification claimed processes for producing a vast class of compounds and the resulting substances. It represented that the class possessed therapeutic value, while giving sulphathiazole and sulphamethylthiazole as the only detailed examples.

The respondent petitioned for revocation. Jenkins J revoked the patent and refused the appellants leave to amend the specification so that it would claim only the two named drugs. The Court of Appeal unanimously affirmed that refusal. The appellants accepted that revocation could not be resisted unless the amendment was allowed.

The central issue before the House was whether the proposed amendment was prohibited by section 22 of the Patents and Designs Acts 1907 to 1946 because it would make the specification claim an invention substantially different from that originally claimed.

1. Appeal dismissed by a majority of three to two. Lord Simonds, Lord Normand and Lord MacDermott held that the proposed amendment was prohibited by section 22 of the Patents and Designs Acts 1907 to 1946. Lord Morton of Henryton and Lord Reid dissented. The Court of Appeal’s order was affirmed, and the appellants were ordered to pay the respondent’s costs.

2. Per Lord Simonds and Lord Normand, the comparison required by section 22 is between the inventions asserted by the original and amended specifications. Each specification must be read as a whole, including its body and claims. The comparison is not confined to the boundaries of the monopoly expressed in the claims.

3. Per Lord Normand, ordinary principles of documentary construction apply. Expert evidence may explain technical language so that the court can understand the specification as its skilled addressee would. Such evidence cannot contradict or modify the document’s natural meaning. Once the specifications have been construed, relevant extrinsic evidence may assist in deciding whether the inventions differ substantially.

4. Per Lord Simonds, the original specification claimed a generic invention comprising the manufacture of a vast range of compounds and represented that all possessed therapeutic value. The two named drugs appeared only as illustrations of that generic quality. The amended specification would instead claim two particular drugs whose therapeutic value depended upon characteristics peculiar to them.

5. Per Lord MacDermott, the original invention rested upon an asserted scientific truth that all products within the defined genus would possess therapeutic value. The amended invention rested upon separate empirical discoveries concerning two tested substances. The different inventive steps revealed a wide and fundamental difference between the inventions.

6. The fact that the two drugs were fully described in the original specification did not determine whether they constituted the same invention. The question was one of fact and degree, applying a broad, common-sense assessment. Removing the whole generic invention and substituting two specific empirical discoveries changed the centre of gravity of the invention and produced a substantial difference.

7. Lord Morton and Lord Reid would have held the amendment competent. In their view, the two specifically described drugs were the preferred embodiment, or a clearly distinguished part, of the wider invention. The amendment merely disclaimed the remainder. Because the majority found the amendment incompetent, the House did not decide whether leave should otherwise have been refused as a matter of discretion.

1. House of Lords: By a majority of three to two, dismissed the appeal and affirmed the Court of Appeal’s order refusing leave to amend the patent specification.
2. Court of Appeal: Lord Greene MR, Somervell LJ and Evershed LJ unanimously affirmed Jenkins J’s refusal of leave to amend.
3. High Court: Jenkins J revoked the patent and refused the patentees leave to amend its specification. The patentees accepted that revocation could not be resisted unless leave to amend was granted.