90 PATHOLOGY. 



its effete constituents removed by the various excretory organs. 

 When any of these conditions are absent, or when, as sometimes 

 happens, the waste of tissue is so rapid as to preclude the elimi- 

 nation of all its products, a mal-condition of the blood-mass is 

 induced, which may lead to grave local complications and 

 diseases of important organs. 



Some chemists hold the opinion that urea more especially is 

 derivable from waste of tissue only, and not from any change or 

 metamorphosis in the chyle or blood. I shall, however, endea- 

 vour to prove that an ursemic condition of the blood may be 

 caused by chyle imperfect in quality or excessive in quantity ; 

 the imperfection of the quality being the result of disordered 

 digestion, or of the ingestion of food unfitted for healthy chylifi- 

 cation; and excessive in quantity from the animal being fed 

 upon aliment too rich for its requirements. In order to under- 

 stand this, however, the student must be made still further 

 acquainted with the process of nutrition, and tins may be 

 divided into — (1.) The introduction into the stomach and ali- 

 mentary canal of the food to be digested : (2.) The formation of 

 the chyle and blood, and the changes which the latter undergoes 

 in the lungs: (3.) The passage of nutritive plasma from the 

 blood to be transformed into tissues: (4.) The metamorphosis 

 and re-absorption of the tissues: (5.) The excretion of these 

 effete materials from the body by the various excretory organs. 



I shall, however, confine myself, very briefly, first, to the 

 digestion of the food, and the formation of the chyle ; and second, 

 to the changes and transformation of the chyle and blood in the 

 vessels. 



All kinds of food are resolvable into carbon, hydrogen, oxygen, 

 nitrogen, and mineral constituents ; and food to maintain the 

 animal body in a state of health must contain all these various 

 substances in due and jiroper proportions, and in quantities 

 depending upon its necessities and wants under the circum- 

 stances in which it is placed, the amount of work it is compelled 

 to perform, the amount of air it breathes, and upon various 

 peculiarities affecting its powers of digestion, whether the animal 

 be carnivorous, omnivorous, or herbivorous. 



It is immaterial to what natural order the animal may belong, 

 the proximate chemical principles required for its nourishment 

 are the nitrogenous — albuminous, non-nitrogenous — starch, gum, 



