226 A Manual of Veterinary Physioloyy. 



These latter figures corresponded to a daily increase of : 



lbs. 

 Albumin - - - '-184 



Fat - - -U17 



Salts - - -022 



Water - - 1157 



Metabolism. — By this term is understood the changes 

 occurring in living tissues. 



It is evident, from all that has been said, that constant 

 breaking down and building up is occurring in the 

 body : every muscular contraction, every respiration, the 

 beating of the heart, the movements of the bowels, all 

 mean wear and tear, and as rapidly as a part is destroyed 

 it must be replaced. The processes of construction and 

 destruction are known as anabolism and katabolism ; in a 

 perfect state of health they should be in equilibrium. 

 Both are dependent upon definite chemical changes oc- 

 curring in the system, some of which we have a fair know- 

 ledge of; others are wrapped in obscurity. 



We have followed the constructive processes from the 

 mouth until the elements of the food pass into the tissues; 

 we have no knowledge of what there endows them with life. 

 We have traced the products of katabolism from the tissues 

 to the lungs and kidneys, and in a future chapter will state 

 what is known of the immediate processes in the muscular 

 tissue, whereby the living substance becomes destroyed, 

 and is cast off from the body through the excretory 

 channels previously dealt with. 



Of the total amount of carbon which enters the body 

 with the food, by far the largest quantity is excreted by the 

 lungs; a certain though small proportion is given oil* from 

 the skin, and in animals which sweat, as the horse, the 

 amount passing off during work may not be inconsiderable ; 

 the remainder of the carbon is got rid of in the form of urea. 

 hippuric or benzoic acids, and minor carbon compounds. 



The hydrogen of the body is excreted as water, the 

 oxygen as carbonic acid and water, only a small proportion of 

 it being returned in the lowest form of oxidation, viz., urea. 



