250 BACTERIA IN INFECTIOUS DISEASES. 



a culture-fluid maintained at a fixed temperature ; 

 but, under these circumstances, is a tissue, the 

 histological elements of which present a certain 

 vital resistance to pathogenic organisms which may 

 be introduced into the circulation. 



If we add a small quantity of a culture-fluid 

 containing the bacteria of putrefaction to the blood 

 of an animal, withdrawn from the circulation into 

 a proper receptacle, and maintained in a culture- 

 oven at blood-heat, we will find that these bacteria 

 multiply abundantly, and evidence of putrefactive 

 decomposition will soon be perceived. But, if we 

 inject a like quantity of the culture-fluid with its 

 contained bacteria into the circulation of a living 

 animal, not only does no increase and no putrefac- 

 tive change occur, but the bacteria introduced 

 quickly disappear, and at the end of an hour or 

 two the most careful microscopical examination 

 will not reveal the presence of a single bacterium. 

 This difference we ascribe to the vital properties 

 of the fluid as contained in the vessels of a living 

 animal ; and it seems probable that the little 

 masses of protoplasm known as white blood cor- 

 puscles are the essential histological elements of 

 the fluid, so far as any manifestation of vitality is 

 concerned. 



The writer has elsewhere suggested that the 

 disappearance of the bacteria from the circulation, 

 in the experiment above referred to, may be 

 effected by the white corpuscles, which, it is well 

 known, pick up, after the manner of amoebae, any 



