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 organisms 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 relation 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 contagious.
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;