22 BACTERIOLOGY 



The main point, however, that had occupied the attention 

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

 two hundred years subsequent to Leeuwenhoek's discoveries 

 was the origin of the "animalcules." Do they generate 

 spontaneously, or are they the descendants of preexisting 

 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 attention 

 developed spontaneously as the result of vegetative changes 

 in the substances in which they were found, attempted to 

 demonstrate by experiment his reasons for holding 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 

 Needham's experimental methods, and demonstrated that 

 if infusions of decomposable vegetable matter be placed in 

 flasks, which, alter being hermetically sealed, were heated 

 for a time in boiling water, no living organisms would be 

 detected in them, 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 promptly met by Spallanzani when 

 he gently tapped one of the flasks that had been boiled 

 against a hard object until a minute crack was produced; 

 invariably organisms and decomposition appeared in the 

 flask thus treated. 



