Fermentation and Kindred Phenomena. 107 



is caused by organisms, and such organisms we know can be 

 cultivated for any length of time in a suitable nourishing medium 

 outside the body (provided it is renewed from time to time) ; 

 how is it, I say, that we ever get rid of the disease ? For our 

 blood and tissues are constantly being renewed ; a suitable 

 pabulum is thus maintained for the continued growth of the 

 disease organisms, and therefore it would seem that when once 

 introduced they should continue to exist and never be got rid 

 of. But we know that the contrary is the case, at least as a 

 rule. Either the patient dies or recovers (quickly very often) 

 and loses all trace of the malady. How can his recovery be 

 accounted for ? 



The explanation may be as follows : — We know that organisms 

 multiply very quickly in a suitable medium, and that the sub- 

 stances they produce are in many cases singularly antagonistic 

 to their existence. The yeast cell is killed when immersed in 

 a solution of spirit of a certain strength, and indol, skatol, and 

 phenol, bodies which are produced by certain putrefactive 

 organisms, are among the most powerful agents in arresting 

 putrefaction. Therefore it is not impossible that the disappear- 

 ance of an infectious disease and the recovery of the patient 

 may be due to some such action : the organisms causing the 

 disease multiplying rapidly up to a certain point, until, in fact, 

 they have produced so much of their peculiar virus that it 

 reacts upon themselves, and poisons off the whole crop. 



But there is another explanation which is perhaps more 

 satisfactory. We know that organisms require certain definite 

 substances for their nourishment, and that therefore they thrive 

 in a culture fluid only so long as these substances are present. 

 Let us suppose that in the tissues of a healthy individual, a 

 small quantity only of one of these principles is present : he 

 catches an infectious disease, organisms are produced in abun- 

 dance in his system, and rapidly use up this small quantity, then 

 it is exhausted, the organisms no longer thrive, and eventually 

 perish. It may be that a very long time will elapse before the 

 convalescent can again accumulate the particular principle which 



