41 



question from more than one standpoint has aided usually in ar- 

 ri\ing at the truth. 



A careful examination into the nature, the structure and the func- 

 tions of the animal system, hai revealed among others the following 

 facts : — 



First ; The organic portion of the animal system consists of two 

 classes of compounds. One class is characterized by the constant 

 admixture of the element nitrogen, and on that account the sub- 

 stances belonging to it are commonly called nitrogenous. They are 

 the main constituents of the blood, and form the muscles and the 

 flesh. The second class of comj)ounds is characterized by the ab- 

 sence of the element nitrogen, and are usually called non-nitrogen- 

 ous, or respiratory substances, and are particularly represented by 

 fat in its various forms. 



Second ; The same portions of elementary bodies, which consti- 

 tute the various organs of the animal system at a given time, do 

 not constitute them for aU times. They fulfill certain functions 

 only for a shorter or longer j^eriod of time, and cease, sooner or 

 later, to be of any value for the maiutainance of normal animal hfe. 

 They are subsequently, in consequeoce of a peculiar process of dis- 

 integTation, secreted in various forms and in various ways, and are 

 continually replaced in the form of food. 



Third : The process of respiration is the main source of animal 

 heat, and resembles closely in its mode of action the well-known pro- 

 cess of combustion. Among its final results most important are a vast 

 amount of carbonic acid and water, which are also the results of the 

 artificial combustion of starch, sugar, fat and similarly constituted 

 articles, under the influence of a sufficient amount of oxygen, the 

 active portion of air. Substances hke starch, sugar, gums, cellulose, 

 fats and oils of every description, in fact all such substances as con- 

 sist of carbon and hydrogen, with or without oxygen, and which 

 are known to chemists as carbo-hydrates and hydro-carbons, (with 

 but a few exceptions) are capable of supporting the process of respi- 

 ration. 



Fourth. The process of nutrition, consists mainly in the build- 

 ing up of bone and muscle during the pei'iod of growth, and the 

 replacement of the tissues which have been wasted in the support 

 of the mechanical force exerted. A successful nutrition depends on 

 the consumption of such nitrogenous substances as are known by 

 the collective name of albuminous compounds. These albuminoids 



