The term "pneumatic differentiation" was first used by the author, in an article which appeared in the New York Medical Record, January 17, 1885. In this article, or in a subsequent one, certain improvements were spoken of which promised to enlarge large the scope of the process there described. This paper is written for the purpose of giving a fuller description of what has now come to be known as the "Pneumatic Differential Process."
Pneumatic differentiation is the mechanical expression of the thoughts and ideas of two men, a physicist and a physician. However parallel their work may have been to earlier investigators, the labor has been entirely independent, and perhaps for this reason there comes a point of divergence which carries their investigations considerably beyond the labors of Hawk, Lange, Junod and Waldenberg. The cabinet in the hands of lung specialists is capable of nice and skillful adjustment to