ZYMOTIC DISEASES have been already referred to, and the most important of them are mentioned in the article NosoLooy. The class of diseases to which Dr. Farr has assigned this now generally accepted term comprises those which are epidemic, endemic, and contagious, as. for example, fever, small-pox, plague, influenza, cholera, Itooping-cough, etc. As Dr. Farr observes: The diseases of this class distinguish one country from another, or one year from another; they have formed epochs in chronology; and as Niebuhr has shown, have influenced not only the fate of cities, such as Athens and Florence, but of empires; they decimate armies and disable fleets; they take the lives of criminals that justice has not condemned; they redouble the dangers of crowded hos pitals; they infest the habitations of the poor, and strike the artisan in his strength down from comfort into helpless poverty; they carry away the infant front the mother's breast, and the old man at the end of life; but their direst eruptions are excessively fatal to men in the prime and vigor of ago. They are emphatically called the morin It must notbe assumed, as the origin of the word (zyme, the Gr. for a ferment) might lead the reader to infer, that all the so-caned zymotic diseases are true fermentations, for the class is intended to comprehend all the principal diseases which have prevailed as epi demics or endemics, and all those which are communicable either by human contact or by animals in a state of disease, as well as the diseases that result from the scarcity and the deterioration of the necessary kinds of food, or from parasitic animals. The diseases of this class thus arrange themselves into the four orders of Iniasmatic, enthetic, dietic, and parasitic disorders, of which fever, syphilis, scurvy, and worms may be regarded as the types.
Dr. Carpenter, in a memoir on the Predisposing Causes of Epidemics, shows that the conditions which give rise to zymotic diseases may be referred to the three following categories: (1.) Conditions which tend to introduce into the system decomposing matter
that has been generated in some external source, as, for example, putrescent food, water contaminated by sewage or other decomposing matters, and air charged with miasmatic emanations. (2.) Conditions which occasion an increased production of decomposing matter in the system itself. The best example of this class of conditions is afforded in the puerperal state (or childhed), in which the tissue of the womb is undergoing rapid disintegration, and the decomposing matters which would be harmless at other times, are now able to act upon the blood of the woman, so as to induce that most fatal of all the zymotic diseases, puerperal fever. (3.) Conditions which obstruct the elimination of the decomposing matter normally or excessively generated within the system, or abnor mally introduced into it from without. For example, any obstacle to the elimination of urea or uric acid, carbonic acid, binary matters, lactic acid, etc., gives rise to as true poisoning as if these substances had been injected into the blood-vessels. The most important of the laws by which zymotic poisons are governed are noticed in the article Yucca.
The average annual rate of mortality in this country at the present time is nearly 22 per 1000, or 1 in 45 of the population; and the deaths from zymotic diseases vary from 21 to 26 per cent (or amount to nearly one-fourth) of the total number of deaths. Taken in order of their greatest fatality they would be thus arranged: cholera, typhus and other forms of continued fever, scarlatina, hooping-cough, measles, croup, small-pox, dysen tery, and erysipelas—the other diseases being less fatal.—For further information on the subjeet of this article, the reader is referred to Aitken's Science and Practice of See Gram T/IEORY OF DISEASE.