PASTEUR, KOCH, AND OTHERS 293 



however, not being amenable to scientific tests, is theoretical, 

 and therefore, so far as the evidence goes, we may safely say 

 that the spontaneous origin of life under present condi- 

 tions is unknown. 



Practical Applications. There are, of course, numerous 

 practical applications of the discovery that the spoiling of 

 putrescible fluids is due to floating germs that have been 

 introduced from the air. One illustration is the canning of 

 meats and fruits, where the object is, by heating, to destroy 

 all living germs that are distributed through the substance, 

 and then, by canning, to keep them out. When this is 

 entirely successful, the preserved vegetables and meats go 

 uncontaminated. One of the most important and practical 

 applications came in the recognition (1867) by the English 

 surgeon Lister that wounds during surgical operations are 

 poisoned by floating particles in the air or by germs cling- 

 ing to instruments or the skin of the operator, and that to 

 render all appliances sterile and, by antiseptic dressings, 

 completely to prevent the entrance of these bacteria into 

 surgical wounds, insures their being clean and healthy. 

 This led to antiseptic surgery, with which the name of Lister 

 is indissolubly connected. 



THE GERM-THEORY OF DISEASE 



The germ-theory of disease is another question of general 

 bearing, and it will be dealt with briefly here. 



After the discovery of bacteria by Leeuwenhoek, in 1687, 

 some medical men of the time suggested the theory that con- 

 tagious diseases were due to microscopic forms of life that 

 passed from the sick to the well. This doctrine of contagium 

 vivum, when first promulgated, took no firm root, and grad- 

 ually disappeared. It was not revived until about 1840. 

 If we attempt briefly to sketch the rise of the germ-theory of 



