CAUSES OF DISEASE. 13 



well shown in the experiments of Majendie and others. Dogs, 

 geese, donkeys, and other animals, when fed entirely on sugar, 

 gum, starch, oil, or butter, died with symptoms of starvation, 

 almost as soon as if they had been kept without food. Even bread, 

 when too fine, is insufficient nourishment. A dog fed on pure 

 white bread lived only fifty days, whereas another fed with the 

 coarsest brown bread was well nourished, and seemed capable of 

 living for an indefinite period. Again, according to the researches 

 of a Commission of the French Institute, animals fed on pure fibrin 

 or albumen died of starvation, almost as soon as if not fed at all. 



Experiments have proved that in order to support health and 

 strength it is essential that, in addition to water, food contain at 

 least three classes of constituents, namely — {1st.) Nitrogenous, to 

 nourish muscular and other albuminoid tissues : {2d.) Hydro- 

 carbons and carbo-hydrates, which undergo combustion in the 

 body, and assist in the maintenance of animal heat and in the 

 assimilation of the nitrogenous compoinids; and {od.) Salines, 

 to supply materials for the building up of the solid structures of 

 the body, maintaining them in health, and assisting in the pro- 

 cesses of assimilation and elimination, conveying new materials 

 into the system and removing old ones out of it. If these various 

 constituents are deficient, absent, or present in undue quantities, 

 health cannot be maintained, and common experience has taught 

 that all animals are kept in the best health when fed on a mixed 

 diet And as types of all proper food we have two examples. 

 {1st.) Milk offers us the best example, as it contains casein — 

 nitrogenous, oil and sugar — hydrocarbons, water and salts. 

 Hence young animals thrive best, and are maintained in health 

 by the food which nature has provided for them. {2d.) Grass 

 may also be adduced as a food containing exclusively all the 

 ingredients required for the support of animal life. 



As examples of the bad effects of food good in itself, but ill- 

 proportioned in quality,, we may adduce those diseases, namely, 

 fatty degeneration of the liver and ancemia, so commonly met 

 with in sheep too exclusively fed on turnips. During good 

 seasons, when the turnips are firm, well-grown, and healthy, they 

 tend to overload the system with saccharine matter, and to induce 

 a degenerative change in the liver, which renders it of a palish 

 yellow colour, friable, and incapable of performing its functions. 

 This condition may be associated with fatness : indeed sheep 



