72 FERMENTS AND MICRO-PARASITES. 



the germs. Schwann also in 1837 made similar experi- 

 ments ; he freed the entering air from the organisms by 

 heating it .strongly. At a later period Schroder and von 

 Dusch attempted to remove the putrefactive germs from 

 the air by simple mechanical means, for example by 

 filtering the air through cotton wool; this was com- 

 pletely successful, and no putrefaction occurred in 

 vessels containing boiled putrescible materials and 

 plugged with cotton wool. Hoffmann, and later Chev- 

 reuil, and in 1862 Pasteur obtained the same result by 

 drawing out the neck of the flask used for the experi- 

 ment, and bending it several times acutely. 



The weight of all these experiments was much 

 enhanced by the fact that control experiments were 

 made in which the same fermentescible fluids were 

 employed, and treated in the same way (by prolonged 

 boiling, &c.)i only with this difference, that the air 

 entered the vessels without being previously deprived of 

 its germs by filtration or by destructive agents. In 

 these control-experiments fermentation or putrefaction 

 always occurred ; and the same result was obtained if 

 the protective arrangements were subsequently removed 

 from vessels which had been preserved free from germs 

 for a long time, and the entrance of germ-laden air 

 was permitted, or when germs were intentionally sown 

 from other putrefying fluids. 



These experiments were repeated later on a gigantic 

 scale in the preservation of articles of food ; scarcely any 

 biological experiment has been so extensively carried out, 

 and has furnished such a uniform result. If fermen- 

 tescible substances are treated by methods which are able 

 to destroy existing organised germs, and if the entering 

 air, and everything that will eventually come in contact 

 with these substances, is treated in such a way that no 

 organised living germs can enter, neither fermentation 

 nor putrefaction occurs ; if any of these precautions are 

 omitted, and the entrance of germs is allowed, then 

 fermentation takes place. It is true, as may be remarked 

 here in passing, that at a later period contradiction of 

 these experiments and their results was not wanting. 



