NUTRITION 



349 



In this case the animal lost 8-2 grammes nitrogen and 225-1 

 grammes of carbon more than it received in the food. 



8*2 grammes nitrogen = 49-2 grammes protein. 

 225- 1 grammes carbon = 259*0 grammes fat. 



In this example of the balance of matter it is evident the diet 

 was insufficient, and the extent to which this was so, both in 

 nitrogenous and non-nitrogenous substances, is revealed. Up 

 to this point the use of the calorimeter is not very evident, nor 

 can we in this place conveniently discuss the point, as it is con- 

 cerned, not with the balance of matter, such as is determined 

 above, but with the balance of energy, which will be considered 

 presently. 



When the income of the body in food balances the expenditure, 

 the body is in equilibrium ; if the income is in excess of the ex- 

 penditure, the body gains weight ; if the expenditure exceeds the 

 income, as in the above example, the body loses weight. 



Metabolism. — By this term is understood the changes occurring 

 in living tissues. It is evident, from what has been said, that 

 constant breaking down and building up is taking place in the 

 body. Every muscular contraction, every respiration, the beat- 

 ing of the heart, and the movements of the bowels, all mean wear 

 and tear, and as rapidly as a part is destroyed it must be replaced. 

 The process of construction is known as anabolism, and of de- 

 struction as katabolism. In a perfect state of health these should 

 be in equilibrium. Both repair and destruction are dependent 

 upon definite chemical changes occurring in the system, of some 

 of which we have a fair knowledge, while others are wrapped in 

 obscurity. 



The metabolism of the tissues is apparently under the influ- 

 ence of the nervous system. We have previously studied a good 

 example of this in dealing with the secretory nerves of the sub- 

 maxillary gland, and it is probable, though our information on 

 the point is very defective, that the nutrition of the body is 

 largely maintained under the guiding influence of the nervous 

 system. We constantly observe muscular wasting in some forms 

 of lameness and injury in the horse, which is out of all propor- 

 tion to the atrophy a part suffers by being simply thrown out of 

 use, and it can only be explained by injury to the trophic nerves 

 which regulate the nutrition of the part. Even a better example 

 is the peculiar changes which sometimes follow direct injury to 

 trophic nerves, as in plantar neurectomy of the horse. The 

 sloughing of the entire foot, or gelatinous degeneration of the 

 phalanx, is due to injury of the trophic nerves. Injuries to the 

 fifth pair of nerves have been followed by sloughing of the cornea, 

 and pneumonia has followed division of the vagi, in both cases 



