18 BACTERIOLOGY. 



Leeuwenhoek's discoveries, was the origin of these 

 bodies. Do they generate spontaneously, or are they 

 the descendants of pre-existing creatures of the same 

 kind? was the all-important question. Among the 

 participants in this discussion were many of the most 

 distinguished men of the day. 



In 1749 Needham, who held firmly to the opinion 

 that the bodies which were creating such a general 

 interest developed spontaneously, as the result of vege- 

 tative changes in the substances in which they were 

 found, attempted to demonstrate by experiment the 

 grounds upon which he held this view. He maintained 

 that the bacteria which were seen to appear around a 

 grain of barley which was allowed to germinate in. a 

 watch-crystal of water, which had been carefully cov- 

 ered, were the result of changes in the barley-grain 

 itself, incidental to its germination. 



Spallanzani, in 1769, drew attention to the laxity of 

 the methods employed by Needham, and demonstrated 

 that if infusions of decomposable vegetable matter were 

 placed in flasks, which were then hermetically sealed, 

 and the flasks and their contents allowed to remain for 

 some time in a vessel of boiling water, neither living 

 organisms could be detected nor would decomposition 

 appear in the infusions so treated. The objection raised 

 by Treviranus, viz., that the high temperature to which 

 the infusions had been subjected had so altered them 

 and the air about them, that the conditions favorable to 

 spontaneous generation no longer existed, was met by 

 Spallanzani by gently tapping one of the flasks that 

 had been boiled, against some hard object until a 

 minute crack was produced ; invariably organisms and 

 decomposition appeared in the flask thus treated. 



