The Black Death was often fatal on the first day of the attack—generally on the third or fourth. In England it was sometimes fatal within twelve hours, and frequently in two days, particularly when spitting of blood or any other form of hœmorrhage was amongst the early symptoms.
The violent inflammatory fever which characterized the Sweating Sickness, generally ran its course in a few hours; in severe cases, indeed, the crisis was always over within a day and night, but it often proved fatal in six hours.
In our own day we have witnessed many instances in which Epidemic Cholera was fatal within twelve hours. I have known several in which the fatal event followed in ten hours, the patient having been within an hour of the dreaded attack in apparent health.
In all great epidemics the protraction of the disease beyond three or four days is a favourable omen. One of the objects in the treatment of the sick is to gain time. If Nature’s first violent effort to expel the enemy that has taken possession of the system, does not destroy life, the vital powers rally, and the frame often survives the storm.
10. Lastly, Epidemics resemble each other in being produced by the same causes. The whole tenor of experience shows that whatever produces an especial liability to one epidemic, produces a similar liability to every other.
The Causes of epidemics, as of all other diseases, are divided into two classes,—the predisposing and the primary. The predisposing causes are those circumstances which bring the body into a fit state for the action of the primary. The primary cause is the agent which directly and immediately excites the disease.
If a number of persons, in an ordinary state of health, say a hundred, are exposed to the primary cause of any epidemic—to the poison of Cholera for example—probably not more than ten would be seized with the disease. Why do the ninety escape? The poison, by the supposition, encompasses and acts upon all alike: why do ten only suffer? Suppose these same hundred persons took a large dose of arsenic, or an over-dose of chloroform, not only would not one in ten escape, but every individual would certainly perish.
It is conceived that the primary cause cannot take effect unless the system be in a state of susceptibility to its action; that there is in the body an innate power of resistance to all noxious agents of this kind, rendering it, when in full vigour, invulnerable to them; that there are certain circumstances which weaken or destroy this resisting power, and which even impart to the body a peculiar susceptibility to the influence of such agents—and these circumstances are called predisposing causes.
The predisposing causes of epidemics may be divided into two classes—External and Internal. The external are those which vitiate the atmosphere; the internal are those which more immediately vitiate the blood.
The vitiators of the atmosphere include overcrowding, filth, putrescent animal and vegetable matters of all kinds, exhalations from foul cesspools, sewers, rivers, canals, ditches, marshes, swamps, &c. Causes of this class are also called localizing, because they favour the generation and spread of epidemics in the localities in which they abound.