94 The Conditions of Infusorial Life. 



the atmosphere imist be so encumbered by its germs, tliat if we 

 add those of other infusoria in similar proportion, we should 

 have the air so crammed with them, that it would almost reach 

 the density of iron. This remark affords an illustration of 

 the good effect of such controversies, for it led to a complete 

 rectification of the thoughtless assertions often made on the 

 abundance of germs ■ and other experiments placed the question 

 upon a very different footing, as we shall see when we come to 

 the part taken in this scientific warfare by M. Pasteur. In an 

 endeavour to convict the germ party of absurdity, M. Pouchet 

 took a large quantity of beef, divided it into three portions, and 

 placed them in three separate vessels of water, covered with 

 plates of polished glass, leaving an air space of one millimetre* 

 (about a three hundredth of an inch) . One of these vessels was 

 put in the roof of the Museum of Natural History, another left 

 in a laboratory on the * second floor, and the third placed on 

 the ground floor. In three days each glass was filled with one 

 species of little monad (M. crepusculum), to such an extent that 

 if they were to be accounted for by the fall of atmospheric 

 germs, M. Pouchet estimates that more than sixty-two millions 

 must have existed in each cubic millimetre of air. Of course 

 the germ theory does not necessarily demand such an abundance 

 of eggs, and the experiment is a proof of fecundity rather than 

 of anything else. 



Observations of what takes place in close vessels are essential 

 to a comprehensive view of the conditions of infusorial life. If 

 air is entirely excluded, we cannot expect to find that any will 

 be developed, unless under special circumstances, like the 

 butyric fermentation, to which allusion has been made. 

 Messrs. Schultze and Schwann published some experiments, 

 in Poggendorffs Annals, in 1837, tending to show that if a 

 maceration was well boiled, and no air admitted except what 

 had either passed through fire or sulphuric acid, no infusorial 

 life would appear. To these M. Pouchet opposed new observa- 

 tions repeatedly performed with great care. M. Schultze placed 

 some vegetable and animal substances in a flask with distilled 

 water, which was boiled to destroy any germs. Two tubes, 

 furnished with bulbs, passed through the cork closing the 

 flask. One tube contained sulphuric acid, and the other a 

 solution o*f caustic potash, so that all air transmitted through 

 them would come into contact with these destructive substances. 

 The experimenter passed air through the tube every day for 

 two months, during which no form of life appeared, although 

 abundance was developed in a similar flask in the same situation 

 which had free access to the atmospheric. Eepeating this ex- 

 periment with the precaution detailed in his work, M. Pouchet 



* The millimetre is -03937 of an English inch. 



