10 



MAINTENANCE RATIONS OF FARM ANIMALS. 



THE MATERIAL KATABOLIZED. 



Ash. — The fasting organism suffers a continual loss of the so-called 

 ash ingredients of its tissues, including both the sulphur and phos- 

 phorus of its proteins and the more distinctly "mineral" elements, 

 such as sodium, potassium, calcium, magnesium, chlorin, etc. These 

 elements are just as essential to the existence of the animal as are 

 the carbon, nitrogen, hydrogen, and oxygen of the so-called " or- 

 ganic " compounds. 



The study of this branch of the subject, however, has hardly pro- 

 gressed far enough as yet to permit a definite formulation of the ash 

 requirements of domestic animals. The present paper, therefore, will 

 be confined to a discussion of the maintenance requirements in the 

 more limited and customary sense, including only those substances 

 whose function it is wholly or in part to serve as sources of energy. 



Fat. — It is a familiar conception that fat formation is the body's 

 method of disposing of surplus feed, and that the body fat is a 

 store of reserve fuel material. The converse of this fact is equally 

 familiar. The fasting or insufficiently fed animal loses fat and may 

 reach a stage of extreme emaciation before the active tissues fail 

 to perform their duties. Obviously, the fasting animal lives very 

 largely upon its reserve fat. These conclusions from common obser- 

 vation have been fully confirmed by comparative analyses of the 

 carcasses of well-fed and of fasted animals as well as by the results 

 of balance experiments in which the exact nature of the outgo from 

 the body has been determined. 



Carbohydrates. — In addition to fat, the body stores up more or 

 less nonnitrogenous matter in the form of glycogen in the liver and 

 muscles. During the first few days of fasting this store of carbo- 

 hydrates is also drawn upon, as is indicated by the fact that the 

 respiratory quotient tends to approach unity, while later the amount 

 katabolized becomes very small. This is well illustrated by Bene- 

 dict's 1 experiments upon fasting men. The average results of a 

 number of experiments in which men fasted for from two to seven 

 consecutive days were as follows: 



Glycogen katabolized by fasting men — Benedict. 



Glycogen katabolized. 



Day. 



Number 

 of sub- 

 jects. 



Total. 



Per kilo- 

 gram of 



body 

 weight. 



Grams. 



Grams. 



First day.. . 

 Second day. 

 Third day.. 

 Fourth day 

 Fifth day... 

 Sixth day . . 



14 

 2 13 



6 



5 

 2 1 



110.0 

 40.3 

 21.8 

 23.3 

 8.2 

 21.7 

 18.7 



1. 69 

 .62 

 .36 

 .40 

 .14 

 .38 

 .33 



Seventh day 



1 The Influence of Inanition on Metabolism. Carnegie Institution of Washington, D. C, 

 1007, p. 464. 



2 Another subject showed a slight gain of glycogen. 



