ESSAYS ON BACTERIOLOGY. 63 



Fifth. Their protective action may be a direct 

 one, or it may be exerted through certain cells called 

 phagocytes, the former seeming at present the most 

 probable. 



Sixth. J^atiiral or acqiiired immunity may be 

 transferred from one animal to another by the trans- 

 fer of blood serum. 



Seventh. Following out the indications from these 

 facts, sufficient practical sudcess has been achieved to 

 make the most conservative almost an enthusiast, and 

 to furnish ground for a rational hope and expectation 

 of fiirther success. 



The following prediction is made by Ernst: "In 

 spite of the great number of unknown points that still 

 surround this new theory of immunity by defensive 

 proteids, it can already be predicted that it will come 

 out victorious in the stniggle in Avhich it is engaged, 

 with the numberless hypotheses and the old prejudices 

 that surround and encumber this branch of general 

 pathology. It will be victorious, for it has already 

 given certain proofs of its importance by vaccinating 

 and curing animals by means of these defensive pro- 

 teids." 



A brief review now of work done with some of the 

 specific bacteria: 



1. Cholera. — Nothing has really been done to 

 overthrow Koch's previous work. Klein, of London, 

 has expressed skepticism in regard to the comma bacil- 

 lus of cholera as a specific organism, quoting the in- 



