Human Physiology. 361 



epidemic diseases, while courage resists them. Those who 

 attempt to fly from plague or cholera fall victims; those who 

 manfully face them, and help to nurse the sick, commonly 

 escape. Care, the anxiety of the poor about their means of 

 living, reduces their vitality, and makes them an easy prey to 

 the physical causes of disease. Sorrow, grief, jealousy, remorse, 

 thwarted love, or disappointed ambition, all favour the de- 

 velopment of disease, if they do not actually produce it ; even 

 the bird pines to death at losing its mate, and the dog dies on 

 the grave of his master. A broken heart from grief is by no 

 means an imaginary disaster. 



Besides this general view of the causes of disease, it may be 

 well to consider the special causes of particular diseases, and 

 classes of diseases, enumerated in the previous chapter, be- 

 ginning with the first-class, or zymotic diseases. Epidemic, 

 endemic, and contagious diseases have a double origin; first, 

 in the exhaustion and impurity which make the liability to 

 disease; and, secondly, in the contagious matter or determining 

 cause of the particular form of disease. 



Small-pox, for example, is a disease of filth, spreading chiefly 

 in the poorer quarters of large towns, in bad air, and where 

 unhealthy conditions offer the predisposing causes. Such a 

 population is liable to become the victims of any miasma; but 

 there is a special kind of poison or virus which produces the 

 febrile eruptive disease called small-pox. It can be communi- 

 cated by inoculation, by contact, and through the atmosphere. 

 We know nothing of the nature of this determining cause 

 whether it is a vegetable germ, a living animalcule, or something 

 quite different from either. What we know is, that small-pox 

 matter, however carried or blown about, produces small-pox in 

 those who are susceptible to its influence; that measly matter 

 produces measles; that the matter of scarlet-fever produces its 

 kind; and that one will not produce the other. As the clean 

 and healthy, the pure and strong, often entirely escape these 



