28 THE MAIN CURRENTS OF ZOOLOGY 



oped by zoologists as in the notable work of Fritz 

 Schaudinn and others. 



One of Pasteur's early triumphs was the demon- 

 stration of the nature of fermentation (1857). This 

 process, which is so important in physiology, was 

 declared to be due merely to chemical action, but 

 Pasteur showed that it depends on the growth of 

 living micro-organisms, and he won his case against 

 the great opposition of the chemist Liebig. 



Against his inclinations Pasteur was forced into 

 the controversy (with Pouchet), concerning the 

 spontaneous generation of life, and, in 1862, made his 

 decisive and epoch-making demonstrations that life 

 is formed in nutrient fluids only when living germs are 

 allowed to enter from the outside. All this directed 

 attention to the constitution of the floating matter of 

 the air. The impalpable dust that is always present 

 and that shows in the path of a sunbeam through a 

 darkened room is of complex composition besides 

 particles of non-living matter there are living or- 

 ganisms of different kinds in a dried condition. 

 Some of these are harmless and others are disease 

 producing. When floating germs are introduced into 

 canned fruits and meats, they grow and cause them 

 to spoil. Other kinds entering wounds produce 



