ESSAYS ON BACTERIOLOGY. 45 



establishment of this fact at once quickened researcli 

 upon the question whether these new products were 

 not the efficient agents in bringing about the multi- 

 form and striking effects of infection. 



In order to solve the problem, it was necessary to 

 secure the material for experiments free from living 

 germs, and for this purpose two processes have been 

 used, the bacteria under question having been ob- 

 tained artificially in pure culture. In the first proc- 

 ess the cultures were subjected to heat sufficient to 

 kill the micro-organisms. But it was ascertained that 

 the heat might also destroy the delicate substances 

 whose action it was desired to investigate. Recourse 

 was therefore had to the process of filtration, devised 

 by Pasteur and Chamberland, and this, or some modi- 

 fication of it, is now generally recognized as the most 

 reliable method, inasmuch as nothing is destroyed or 

 ■changed, the bacteria are removed, and presumably 

 all of the desired products are secured. Some of 

 "these substances have also been isolated, by definite 

 ■chemical processes, from the infected body or from 

 ■cultures. Brieger has been the leader in this work, 

 but thus far it is confessedly difficult, and has yielded 

 •only incomplete results, since bacterial growth is, as a 

 rule, attended by the formation of several so-called 

 ptomaines or toxins. 



Though the work is beset with difficulties and com- 

 plications, enough has been established to warrant ^he 

 conclusion that the phenomena following infection are 



