Human Physiology. 345 



poisons, as glanders and hydrophobia, are almost inevitably 

 fatal. They do not fasten upon every constitution; every 

 poison of this kind seems to need some kindred element on 

 which to act; but when they declare themselves, the power to 

 combat them is lost. The poison of hydrophobia may lie 

 inert for months, then suddenly burst forth and kill. 



The other diseases of this class, dietic and parasitic, are 

 evidently avoidable. They are diseases of poverty, vice, and 

 dirt; and it is the shame of civilisation and Christianity that 

 hundreds of persons should die every year in London of hunger, 

 of drunkenness, and of filth. It may be doubted if parasites 

 ever fasten upon vegetables or animals in full health. And 

 health is, in fact, the best preventive remedy for all diseases. 



It is important to remark that two elements enter into the 

 production of most, if not all kinds of zymotic, contagious, or 

 epidemic diseases. There is the malaria, miasm, or contagious 

 matter, or the influence, whatever it may be, which determines 

 the specific form of disease, as the contagion of small-pox or 

 scarlatina, typhus or cholera; and there must also be the physi- 

 cal condition which predisposes the patient to be acted upon 

 by the diseasing agent Only a certain, and generally a small, 

 proportion of persons suffer from epidemics. The greater 

 number are protected by the purity of their systems, or the 

 vital force which gives the energy of health. In every case the 

 germ must find something to nourish it the poison, something 

 which cannot resist its action. A healthy man, with unexhaus- 

 ted nervous power and pure blood orie who breathes pure air, 

 lives upon a pure diet, and refrains from all diseasing habits, 

 may pass unscathed through small-pox contagion, yellow-fever, 

 cholera, and defy the influences of deadly malarias. Persons 

 who live upon a simple vegetable diet, and whose habits in 

 other respects are healthful, are very little susceptible to the 

 influence of epidemics. Some cannot be vaccinated success- 

 fully until they go through a course of flesh-eating. In every 



