490 THE WAR WITH THE MICROBES. 



a very active poison, the substance secreted is much less harmful. 

 This is accounted for by the supposition that the glucose is decomposed 

 into acid, which, in its turn, neutralizes or decomposes the poison ordi- 

 narily produced by the germ. These poisons, it was originally sup- 

 posed, resulted from the decomposition of the food of the germ, just as 

 soluble and assimilable albuminoids are produced by the acids and 

 ferments of the animal body from the insoluble albuminoids that are 

 ingested as food. It has been found, however, that in most instances 

 the poison of the germ is in solution in quantity only after the germs 

 themselves have become partially disintegrated. In other words, the 

 active bacterial poisons seem to be products of the cell and retained 

 within the cell until the latter dies and the cell membrane is broken, 

 permitting the passage into the surrounding liquid of the poison. 

 What, then, is the true nature of these poisons if they belong neither 

 to the bases nor to the proteids or toxalbumins? That, unfortunately, 

 is one of the problems to which, up to the present time, chemical 

 research has not been able to give a definite answer; and this because, 

 as we have already noted, the poisons of these bacteria are so tremen- 

 dously active, and consequently produced in proportionately small 

 amount, even when a large quantity of the culture media is used, that 

 it has so far been a matter almost of impossibility to separate a suffi- 

 cient quantity of these poisonous principles to purify them perfectly 

 for chemical analysis. Perhaps this object has been attained more 

 nearly than ever before by some workers in the biochemic laboratory 

 in this city, who have succeeded in separating from cultures of the 

 tuberculosis germ a crystalline poison with constant melting point and 

 a constant composition. This is not the only poison produced by the 

 tuberculosis germ, but that it is one of the principles which is respon- 

 sible for much of the trouble with this disease is beyond doubt. These 

 special poisonous principles, which are so difficult to obtain pure, we 

 designate by the name toxins, to distinguish them from the ptomaines 

 and proteid substances before mentioned. Another difficulty which is 

 always encountered in extracting the poisons of bacteria is their 

 instability. The material with which an experiment is begun may be 

 very j)oisonous, but the processes of precipitation and extraction 

 through which it must be passed in order to obtain a desired substance 

 are such that often, long before the final stages have been reached, the 

 nature of the poisons has undergone an entire change due to the chem- 

 ical processes which have necessarily been applied. 



We have said that the poisons of the germ were synthetic products 

 which were built up within the cell wall. Some of these easily pass 

 through the cell wall, due, probably, to the greater permeability of the 

 living membrane; others are retained within the cell wall, only to pass 

 into solution when these walls are broken down. Tetanus, diphtheria, 

 and swine plague allow this diffusion to take place very rapidly, while 

 with other germs, like typhoid fever, anthrax, cholera, glanders, tuber- 

 culosis, the poison is produced and retained within the cell more firmly 



