INFECTION AND INTOXICATION. 9 



The production of immunity to many bacteria or their pro- 

 ducts is associated with the formation in the animal thus 

 protected of certain antidotal substances which appear in the 

 body fluids. It has been shown that a similar immunity for 

 ricin and abrin can be induced, and more recently the same 

 has been proved for snake venom. In these instances the 

 insusceptibility to the actions of the toxic agents is associated 

 with the appearance in the blood of the treated animals of 

 antidotal bodies capable of affording protection from these 

 toxic proteids. In this connection, I have been able to show 

 that by the exhibition of repeated small doses, rabbits, other- 

 wise highly susceptible, can be made quite resistent to the 

 blood serum of the dog. 



The foregoing considerations teach that, in the study of the 

 causation of disease, a widening knowledge is enabling us to 

 appreciate how much is due to the actions of the living para- 

 sitic agents themselves, and how much to toxic substances 

 derived from these and from other sources. The importance 

 of agents of intoxication is becoming more and more impressed 

 upon us ; and when we reflect that their distribution is co- 

 extensive with organized nature itself, and that they are 

 present in the most vital of our body constituents, we begin to 

 see, if indeed only faintly, what consequences their presence 

 may entail. 



I would bring these remarks to a close by begging you not 

 to forget that although much has been written upon the disease- 

 producing micro-organisms, not a small chapter might be added 

 upon those which are friendly in their nature. When you 

 consider that the phenomena of decomposition and putrefaction 

 are executed through their efforts, that the restoration of the 

 soil, and the fitting of it for the growth of the higher plants, 

 is effected by a special group of bacteria, you will appreciate 

 the fact that life on this globe would be impossible for the 

 higher living forms could these lowly ones be perchance 

 exterminated. 



Furthermore, there are defences set up everywhere in the 

 animal body through which the invasion of these noxious para- 

 sites is resisted. Those parts most exposed to their action 



