peesident's address. 215 



to depend upon such agency, are Asiatic cholera,* typhoid fever, 

 tetanus, anthrax, tuberculosis, leprosy, and diphtheria. Such 

 being the case the very interesting and important question 

 arises : How is it, the germs of these organisms being so subtle 

 and so easily diffusible, that more of us do not fall victims to their 

 attacks ? In answering this question we must remember, in the 

 first place, that the morbific organisms cannot live and multiply 

 except under certain strictly limited conditions. Some of them, 

 as for instance the typhoid bacillus, are killed by exposure to 

 light, others by contact with acid or alkaline fluids, and all of 

 them, probably, are subject to very rigid limitations as to environ- 

 ment. Secondly, an extremely interesting series of observations 

 by Metschnikoff and others have shown it to be probable that, in 

 the healthy condition of the body, the tissue cells are capable 

 of destroying, — eating up, as it were, and assimilating, — any 

 bacteria that may obtain a lodgment about them. And not only 

 this, — by the irritant action of the parasites, the healthy tissue 

 cells are stimulated to extra growth, throwing out round the 

 affected centres numerous active " phagocytes," which thus form 

 a sort of advanced guard ready to attack any fresh battalions of 

 the enemy. And in this way, supposing the assaulted organism 

 to possess sufficient vigour for an unwonted cell-proliferation, 

 the attacking force is destroyed and driven out. But, on the other 

 hand, if the system is enervated at the outset, its cells below 

 par in point of vitality, and especially if the invading host be 

 too numerous, — then the phagocytes become an ineffective force, 

 they die or degenerate, incapable of coping with their antagon- 

 ists, and the fortress may have to surrender at discretion. And 

 though the observations on which these ideas are built still need 

 repetition and confirmation — though they may indeed be proved 

 to be to a considerable extent erroneous, it seems nevertheless 

 likely that they contain germs of truth. They at any rate 

 enable us to understand how it is that a body in vigorous health 

 is able to repel the attacks of infectious Bacteria, and how, when 

 the microbes have effected a lodgment, perfect rest of body and 

 the maintenance of animal heat constitute the most important 



* This is disputed, however, by Dr. Klein. 



P 



