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 tc the well. This doctrine of contagiwm 
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 
