RESISTANCE TO INFECTIOUS DISEASE 13 



ceptible to tetanus poison in the summer but not during the winter 

 sleep. There exist, therefore, different- mechanisms for excluding 

 poisons from the sensitive and reacting cells and among them are 

 certain quantities of neutralizing, or antitoxic substances, normally 

 contained in the blood. "We know at least one such definite antitoxin, 

 namely, the diphtheria antitoxin, which exists in minimal quantities in 

 the blood of man and the horse. 



The absence of numerical relation between the mechanism which 

 destroys bacteria and neutralizes poisons sometimes works sad havoc 

 for the body. The two capacities may differ naturally or are enhanced 

 in different degrees by artificial means. The matter is one of great 

 importance because almost without exception all bacterial diseases are 

 examples of poisoning. The mechanical obstructions produced by the 

 bacterial bodies are relatively unimportant. The body is more readily 

 defended from the invasion of bacteria, with very few exceptions, than 

 from the effects of their poisons. The capacity to dispose of typhoid 

 and cholera bacilli is more easily produced than the power to neutralize 

 or otherwise render innocuous the poisons liberated by the dissolved 

 bacilli. It is precisely because we have not yet learned how to over- 

 come this class of bacterial poisons within the body that we have not 

 mastered the bacterial diseases as a whole. There are, however, certain 

 bacterial poisons for which adequate antidotes are readily produced, 

 thus, for example, for the diphtheria, tetanus, botulism and possibly the 

 dysentery poisons. Here the poisons can be more easily neutralized 

 than the bacilli can be got rid of, but by neutralizing the poisons we 

 succeed in arresting the multiplication of the bacteria and often in 

 curing the disease. 



The normal body possesses a mean resistance to bacterial invasion 

 and to bacterial poisoning which, while somewhat fluctuant, is of high 

 value except under certain exceptional conditions in which infection 

 readily develops. We know that certain general states of and influences 

 exerted on the body are associated with a rise or a fall of this mean 

 value. But we are not equally informed of the physical basis of this 

 rise and fall. This particular topic is peculiarly difficult because of 

 the large numbers of factors which enter into it. We know from 

 observation that proper clothing, wholesome food, good hygienic sur- 

 roundings, avoidance of over fatigue and of depressing psychic impres- 

 sions, and that physical care of the body, all contribute toward main- 

 taining health as the reverse conditions predispose to establishing dis- 

 ease. In seeking the physical basis of this difference we must avoid 

 confusing cause with effect. Good hygienic surroundings may act 

 chiefly by excluding the sources of infection rather than by enhancing 

 resistance. Yet there is experimental as well as observational founda- 

 tion for the belief in these general influences to affect the disposition to 

 acquire or escape infectious disease. Animals which are made to fast, 

 to over-exercise, are made anaemic, are given excessive quantities of 



