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 overcome 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 surroundings, avoidance of over fatigue and of depressing psychic impressions, and that physical care of the body, all contribute toward maintaining health as the reverse conditions predispose to establishing disease. 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 foundation 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 anæmic, are given excessive quantities of