22 BACTERIOLOGY. 



animals dead of splenic fever, and with the progress 

 of kno\\4edge upon the parasitic nature of certain dis- 

 eases of plants, the old question of " contagium ani- 

 matum " again began to receive attention. It was taken 

 up by Henle, 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 earlier 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 attracting such general atten- 

 tion developed spontaneously as the result of vegetative 

 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 appeared about a grain of barley 

 germinating in a carefully covered watch-crystal of 

 water were the result of changes going on 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 heated for a time in a 

 vessel of boiling water, neither could living organisms 

 be detected nor would decomposition appear in the infu- 

 sions so treated. The objection raised by Treviranus, 



