22 PATHOGENIC BACTERIA. 



done After a variable time the previously heated 



fluid within the hermetically-sealed flask swarms more 

 or less plentifully with bacteria and allied organisms, 

 even though the fluids have been much degraded in 

 quality by exposure to the temperature of 212 ° F., and 

 have in all probability been rendered far less prone to 

 engender independent living units than the unheated 

 fluids in the tissues would be.' " 



These somewhat lengthy quotations are of great in- 

 terest, for they show exactly the state of the scientific 

 mind at a period as recent as twenty-five years ago. 



II. CHEMICAL CONTRIBUTIONS; FERMENTATION AND 

 PUTREFACTION. 



As in the biologic world the generation of life was an 

 all-absorbing problem, so in the world of chemistry the 

 phenomena of fermentation and putrefaction were inex- 

 plicable so long as the nature of the ferments was not 

 understood. 



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 time of Leeuwenhoek 

 were living organisms — vegetable forms — capable of 

 growth. 



While yeast was looked upon as an inert substance 

 in the act of fermenting, it was impossible to under- 

 stand how it could impart fermentation to other sub- 

 stances; but when it was learned by Latour that the 

 essential element of yeast was a growing plant, the 

 phenomenon became a perfectly natural consequence of 

 life. Not only the alcoholic, but also the acetic, lactic, 

 and butyric fermentations have been shown to result 

 from the energy of low forms of vegetable life, chiefly 

 bacterial in nature. Prejudice, however, prevented many 

 chemists from accepting this view of the subject, and 

 Liebig strenuously adhered to his theory that fermenta- 

 tion was the result of internal molecular movement which 

 a body in the course of decomposition communicates to 



