18 BACTERIOLOGY. 



Heule, and it was he who first logically taught this 

 doctrine of infection. 



The main point, however, that had occupied the atten- 

 tion of scientific men from time to time for a period of 

 about two hundred years subsequent to 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 covered, 

 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 



