INTRODUCTION. 21 



air is essential to life, and that in his flasks the air was 

 excluded by the hermetically-sealed necks. 



Schulze (1836) set the objection aside by filling a flask 

 only half full of distilled water, to which animal and 

 vegetable matters were added, boiling the contents to 

 destroy the vitality of any organisms which might al- 

 ready exist in them, then sucking daily into the flask a 

 certain amount of air which had passed through a series 

 of bulbs containing concentrated sulphuric acid, in which 

 it was supposed that whatever germs of life the air might 

 contain would be destroyed. This flask was kept from 

 May to August; air was passed through it daily, yet with- 

 out the development of any infusorial life. 



The term "infusorial life" having been used, here it 

 is well to observe that during all the early part of their 

 recognized existence the bacteria were regarded as ani- 

 mal organisms and classed among the infusoria. 



Cagniard Latour and Schwann in the year 1837 suc- 

 ceeded in proving that the minute oval bodies which had 

 been observed in yeast since the the time of Leeuwenhoek 

 were living organisms vegetable forms capable of 

 growth; and when Boehm succeeded a year later in de- 

 monstrating their occurrence in the stools of cholera, and 

 conjectured that the process of fermentation was con- 

 cerned in the causation of that disease, the study of these 

 low forms of life received an immense impetus from the 

 important position which they began to assume in rela- 

 tion to medical science. 



The experiments of Schwann, by proving that the 

 free admission of calcined air to closed vessels contain- 

 ing putrescible infusions was without effect, while the 

 admission of ordinary air brought about decomposition, 

 suggested that the causes of putrefaction which were in 

 the air were living entities. 



In 1862, Pasteur published a paper " On the Organized 

 Corpuscles existing in the Atmosphere," in which he 

 showed that many of the floating particles which he 

 had been able to collect from the atmosphere of his 



