HOW TYPHOID FEVER IS CONVEYED. 463 



them, and they pass out with the changing air. Hence the importance 

 of free ventilation ; and hence one reason why fever should be treated, 

 if possible, in large, airy rooms. Not only is free ventilation good for 

 the sufferer, but it diminishes the risk to the attendants. 



We see in this, too, the reason for banishing bed-curtains, carpets, 

 and all unnecessary furniture from the sick-room in cases of contagious 

 fever. The germs are apt to adhere to such articles, and so make them 

 the means of conveying the disease to others. 



All organisms consume in their growth nitrogen and water. Those 

 with which we are now dealing are no exception to the rule. Growing 

 in the system, they must get these elements there. But nitrogen and 

 water are the chief materials required for the nutrition and repair of 

 the various organs and tissues of the body. The propagation in it of 

 millions of organisms, having wants identical in the main with those of 

 its own tissues, must cause serious disturbance. And so it does. This 

 disturbance declares itself by that aggregate of phenomena to which 

 we apply the term fever. 



An organism which thus grows in and at the expense of another is 

 a parasite. One of the peculiarities of parasites is that they flourish, 

 not in any part of their host, but only in some particular organ or 

 tissue, which is called the nidus, or nest of the parasite. The organ- 

 isms with which we are now dealing (the poisons of the eruptive fevers) 

 show similar peculiarities. Each has its own nidus, its own localized 

 habitat, in which it is propagated, and out of which it ceases to be 

 reproduced. The poison of small-pox has its nidus in the deep layer 

 of the skin ; hence its characteristic eruption. That of scarlet fever in 

 the superficial layer of the skin and in the throat ; hence the rash and 

 the sore-throat of that disease. That of measles in the skin and in 

 the mucous membrane of the air-passages ; hence its characteristic 

 symptoms. That of typhoid fever in the glands of the intestine ; 

 hence that disease consists of fever and of ulceration of the bowel. 



The contagiousness of a given eruptive fever must be directly as 

 the number of germs which, in a given time, pass from the body of a 

 sufferer into the surrounding atmosphere. This, in its turn, must 

 depend on the seat of the propagation of the poison, and on the rela- 

 tion which this bears to that atmosphere. In small-pox, scarlet fever, 

 typhus fever, and measles, the seat of this propagation is the skin and 

 mucous membrane of the air-passages ; it is, therefore, in direct, free, 

 and constant communication with the external air. The poisons of 

 these diseases are accordingly freely given off into the atmosphere of 

 the room in which the sufferer is, and they themselves are highly con- 

 tagious. 



In typhoid fever, the poison is propagated in the bowel, and is 

 thrown off with the discharges from it. It thus passes from the system 

 in a manner and in a combination which insure its speedy removal 

 from the neighborhood of the sufferer. The typhoid-germs are there ; 



