In the case of McClain v. Ortmayer, 1891, the U.S Supreme Court dealt with a patent dispute involving improvements to an existing invention. The plaintiff, McClain had patented an improvement on a clamp for trouser seams used by tailors and claimed that Ortmayer's similar device infringed upon his patent rights. However, the court found that while both devices performed essentially the same function in substantially similar ways to achieve identical results, there was no infringement because they were not identical in form or construction. The court ruled that merely changing minor details or proportions without altering principle or mode of operation does not constitute as new invention eligible for separate patent protection under law; hence it did not infringe upon McClain’s patents.

In the dissenting opinion for McClain v. Ortmayer, Justice Lamar disagreed with the majority's interpretation of patent law and its application to this case. He argued that a simple change in form without any improvement in function or efficiency should not be enough to warrant a new patent. In his view, such an interpretation would allow anyone to make minor alterations to existing inventions and claim them as their own, undermining the purpose of patents which is supposed to encourage genuine innovation and progress. Furthermore, he believed that there was insufficient evidence presented at trial proving that Ortmayer’s invention was indeed novel or non-obvious compared with previous designs already patented by others including McClain himself.