66 HEALTH AND DISEASE 



exist, and, to use a common expression, there may be faults on both 

 sides. It becomes necessary, therefore, to take into consideration the 

 fact that what may be called perfect surroundings absolutely adapted 

 for the preservation of health in one animal may prove to be quite in- 

 sufficient to secure the same results in the case of another. Indeed, 

 the favourable conditions in the first case may have a tendency to induce 

 disease in a subject which, from previous habit, or as a consequence of 

 the influences of heredity, may be predisposed to contract certain dis- 

 orders. A single illustration will make this proposition clear. In the 

 case of one animal, the power to sustain extreme cold or extreme heat 

 without suffering may be developed in a high degree. In another animal 

 the system may be particularly obnoxious to cold or heat, and such an 

 animal may suffer from catarrhal diseases which the first animal would 

 entirely escape. 



ORDINARY CONDITIONS OF HEALTH 



Hygiene, although especially concerned with the maintenance of 

 health, by a liberal interpretation may be made to include the means 

 of prevention of certain diseases. It is, however, considered to be more 

 convenient to apply the word " prophylaxis" to the science of pre- 

 vention, although it is impossible to escape the conviction that every 

 care that is taken to keep an animal in a healthy state necessarily in- 

 cludes the adoption of precautions to prevent the inroads of disease, 

 whether common or specific. 



Starting with the presumption that the science of Hygiene is to be 

 applied to animals in a healthy condition and with the object of preserv- 

 ing health in other words, prolonging the animal's life and keeping it 

 in the highest state of efficiency for the work it is called upon to per- 

 form, the question arises: What are the ordinary means by the agency 

 of which this desirable end may be secured? The first thing which 

 suggests itself relates to the function of nutrition. Even in a state of 



DO 



perfect animal idleness the ordinary physiological processes continue; 

 oxidation, that is to say destruction, of tissues is always going on. Every 

 movement of the animal, whether voluntary or involuntary, causes an 

 appreciable amount of tissue waste; the waste products have to be ex- 

 creted, as many of them are of a poisonous character, and the waste 

 has to be replaced by new material. This repair of tissue demands a 

 regular supply of solid and liquid food, containing the necessary materials 

 for purposes of nutrition. Pure food and pure water in appropriate quan- 

 tities are among the first essentials for the maintenance of life and health. 



