GRADUAL DEVELOPMENT OF THE GERM THEORY. 75 



course no value, are of the greatest importance for the 

 questions of abiogenesis, and of the role of the 

 organisms in fermentation and putrefaction. It was 

 only as the result of these experiments that it could be 

 absolutely maintained that spontaneous generation does 

 not take place, and that fermentation and putrefaction 

 do not occur without the aid of minute organisms. 



3. If organisms are the constant cause of fermentation 3. Fermenta- 



T /., i i ,1 t> , tive organisms 



and putreiaction, one must, bearing m mind tne tact occur every- 

 that decomposition of putrescible materials occurs at all ta^feraient- 

 places and at all times (provided that no special means escible sub- 



Sl&HCGS 



are employed to prevent it), come to the conclusion that alway 

 these lower putrefactive organisms are extremely widely 

 distributed, and that thus there is always and every- provided that 

 where opportunity for the infection of putrescible organisms are 

 materials. The further efforts of the advocates of the 

 vitalistic theory were therefore directed to the demon- 

 stration of the presence of organised ferments in all oar 

 surroundings. Investigations which were begun by 

 Ehrenberg, and then continued by Pouchet, Tyndall, 

 Pasteur, Cohn, &c., demonstrated with certainty that 

 the air always contains the germs of fermentation and 

 putrefaction, that dust consists in part of micro-organ- 

 isms, and that water, soil, and in fact all our surround- 

 ings are always contaminated by these minute cells. In 

 recent times the methods, more especially of aeroscopy, 

 have been perfected on the view that the air is the most 

 frequent carrier of the germs, and is the medium which 

 leads most frequently to the infection of fermentescible 

 substances. Later investigations (Sanderson, Rind- 

 fleisch, Cohn, Hiller, Brefeld) have, however, shown that 

 the air in most places contains relatively few active 

 germs, and that the active agents of fermentation are 

 conveyed by solid substances, water, &c., which are 

 contaminated with germs, more frequently than through 

 the medium of the air ; but by this alteration in 

 the views as to the part played by the different media 

 in setting up fermentation there is no change in the 

 doctrine of Pansperinism and of the universal distri- 

 bution of germs in our surroundings. 



