340 MICROSCOPIC PHOTOGRAPHY. [MEMOIR XXV. 



In this manner I made many microscopic daguerreo- 

 types. Some of them, such as were needed, were subse- 

 quently cut in wood to serve as illustrations for my 

 Treatise on " Human Physiology." From that work I 

 extract the specimens on the opposite page. 



When the collodion process was invented, I made 

 many of these photographs in that way. Some of my 

 old original daguerreotypes were exhibited in the Cen- 

 tennial Exposition at Philadelphia, as illustrations of the 

 early history of the art. Collodion photographs have, of 

 course, the great advantage over daguerreotypes in this, 

 that they may be magnified by the lantern and used for 

 demonstration before a large class. 



