Introduction 5 



abundantly in the organism and be distributed in the blood, before 

 they can produce a general morbid condition. The spirillum of 

 human recurrent fever is an example of this. It multiplies for some 

 days and produces several generations without provoking the least 

 malaise ; then, however, their appearance in the blood suddenly 

 produces intense fever and constitutional phenomena of the most 

 pronounced character. 



On the other hand there are certain bacteria which are dis- 

 tinguished by a very much feebler reproductive power, but a more 

 marked toxic activity. Incapable of spreading through the organism, 

 these bacteria remain localised at the point of entrance, where they 

 secrete their poisons and thus frequently set up a fatal intoxication. 

 Some of these bacteria, such as the bacilli of tetanus and of diphtheria, 

 penetrate more or less deeply into the living tissues of the affected 

 animal. Others can manifest their toxic action so to speak at a 

 distance or by simple contact with the living elements. Into this 

 category comes the organism of Asiatic cholera. Koch's vibrio, once 

 established in the intestine, there secretes its poison ; this, absorbed 

 by the apparently intact intestinal mucous membrane, sets up a fell 

 disease, purely toxic in character. It is probable that in the case of 

 those intestinal diseases whose etiology is still unknown, such as 

 infantile choleras, the poisoning by the products of micro-organisms 

 constitutes the essential phenomenon. The micro-organisms do not 

 make their way into the blood or tissues ; they remain in the contents 

 of the intestine and thence set up their deadly intoxication. 



Instances do exist in which the pathogenic micro-organism disap- 

 pears from the body, leaving there a toxin which, alone, is responsible 

 for death. Thus in the spirillar septicaemia of geese, the birds die 

 at a stage when not a single living spirillum can be found in the 

 body. The poisoners have been destroyed before the toxin produced 

 by them had completed its work. In other instances, e.g. typhoid fever 

 of the horse, the specific micro-organism likewise disappears before 

 the death of the animal ; but at the period when the poison of this 

 bacterium finishes its fatal work, there is a secondary invasion of [6] 

 other micro-organisms which have nothing to do with the typhoid 

 fever proper of the horse. 



This great variability in the action of the different pathogenic 

 agents is still further increased through the differing relations between 

 the parasites and the affected organism. Certain micro-organisms 

 are capable of producing a typical disease, whatever may be the 



