20 THE GERM THEORY OF DISEASE. 



causes which kill animals or hinder their development must 

 be opposed to fermentation " (Schutzenberger, page 38). 

 This seems to be the first appearance of the modern germ 

 theory in a definite form, and the first announcement of the 

 true theory of the antiseptics. Astier, however, regarded the 

 living substance as composed of animalcules. A number of 

 observers within the next few years seem to have arrived at 

 the same conclusion. 



SCHWAK 



The next real advance was made about the year 1838, 

 when Schwan and La tour, each independently, took up the 

 microscopic inquiry, with improved instruments, and dis- 

 covered that the granules of yeast were membranous bags, 

 which exhibited all the morphological characters of vegetable 

 cells, and under proper conditions increased and multiplied, in 

 the biological sense. The conclusion was quickly reached by 

 them, that it was the life and growth of the plant which 

 caused the chemical changes of fermentation ; and that the 

 products, carbon dioxide and alcohol, were excrementitious 

 products of the plants. 



At this time Schwan was working on spontaneous genera- 

 tion, which he very distinctly negatived. He also, together 

 with Schultz and Helmholtz, was the first to establish the fact 

 that putrefaction would not occur without the presence of cer- 

 tain minute organisms, which might be destroyed by boiling; 

 and then, that air deprived of these organisms by being heated, 

 or by filtering through sulphuric acid, might be admitted 

 and yet no decomposition would occur. This destroyed the 

 hypothesis previously held, that oxygen was the active agent 

 in decomposition ; yet it was not generally accepted. It is to 

 this discovery that we owe our ability to preserve fruits, 

 meats, etc., in cans hermetically sealed, which has conferred 

 such blessings upon mankind. 



