CHAPTER XXXVI. 



SPOEADIC DISEASES— continued. 



DIETETIC DISEASES. 



In order that the health of the animal body may be duly main- 

 tained, it is necessary that the various kinds of food should be 

 sufficient in quantity and undeteriorated in quality. It is also 

 necessary that the solid food contain at least four classes of con- 

 stituents, each of which plays an important part in supplying 

 the various wants of the economy, either as to supplying 

 materials for tissue formation or for force. These constituents 

 are — (1.) Nitrogen, nitrogenous or proteid food, which seems 

 most fitted to nourish muscular and other albuminoid tissues ; 

 on this account the substance containing it has been called 

 plastic or nitrogenous food. Substances defective in nitrogen, 

 and having an excess of carbon or hydrogen, are called (2.) 

 carbohydrates or starchy foods, consisting of elements which 

 easily break up into carbonic acid and water, supply materials 

 for combustion, and thus assist in maintaining animal heat and 

 other energies required by the system. (3.) Eats, or hydrocarbons, 

 like the carbohydrates, have no nitrogen, require a great supply 

 of oxygen, and evolve a large amount of animal heat. Food must 

 also contain (4.) saline materials, in order that the solid struc- 

 tures of the body be built and maintained in health ; the saline 

 constituents also aid in the processes of assimilation and 

 elimination, of carrying new materials into the system and old 

 materials out of it. If these constituents are absent, or are present 

 in undue proportions, health cannot be maintained, and common 

 experience has taught us that all animals are kept in the best 

 health when fed on a mixture of foods. 



Although chemical analyses have enabled us to know the 

 quantities of nitrogen, carbon, &c. contained in the food, it does 

 not follow (as General Fitzwygram justly remarks) " that the 

 food which possesses these constituents in the greatest abundance 



