October 17, 1913] 



SCIENCE 



539 



of the greatest scientific and practical 

 interest. 



Evidently new ideas are not lacking 

 amongst those who are engaged in investi- 

 gating the role of the proteins and their 

 splitting products in the animal economy. 

 But of more immediate practical interest 

 is the question of the amount of protein 

 required by animals under various condi- 

 tions. It is obviously impossible to fix this 

 amount with any great accuracy, since pro- 

 teins differ so widely in composition, but 

 from many experiments, in which a nitrogen 

 balance between the ingesta and the excreta 

 was made, it appears that oxen remain in 

 nitrogenous equilibrium on a ration contain- 

 ing about one pound of protein per 1,000 

 lbs. live-weight per day. All the British 

 experiments of a more practical nature have 

 been recalculated on a systematic basis by 

 Ingle, and tabulated in the Journal of the 

 Highland and Agricultural Society. From 

 them it appears that increase of protein in 

 the ration, beyond somewhere between one 

 and a half and two pounds per 1,000 pounds 

 live-weight per day of digestible protein, 

 ceases to have any direct infiuence on in- 

 crease in live-weight. 



We may fairly conclude, then, that about 

 two pounds of protein per 1,000 pounds 

 live-weight per day is sufficient for a fatten- 

 ing ox. This amount is repeatedly exceeded 

 in most of the districts where beef produc- 

 tion is a staple industry, the idea being to 

 produce farmyard manure rich in nitrogen. 

 The economy of this method of augmenting 

 the fertility of the land is very doubtful. 

 The question is one of those for the solution 

 of which a combination of accurate experi- 

 ment and modern accountancy is required. 

 Protein is the most expensive constituent of 

 an animal 's dietary. If the scientific inves- 

 tigator, from a study of the quantitative 

 composition of the proteins of the common 

 farm foods, and the economist, from careful 



dissection of farm accounts, can fix an 

 authoritative standard for the amounts of 

 protein required per 1,000 lb. live-weight 

 per day for various types of animals, a 

 great step will have been made towards 

 making mutton and beef production prof- 

 itable apart from corn-growing. 



For many years it has been recognized 

 that an animal requires not only so much 

 protein per day, but a certain qiiota of 

 energy, and many attempts have been made 

 to express this fact in intelligible terms. 

 Most of them have taken as basis the expres- 

 sion of the value of all the constituents of 

 the diet in terms of starch, the sum of all 

 the values being called the starch equiva- 

 lent. This term is used by various writers 

 in so many different senses that confusion 

 has often arisen, and this has militated 

 against its general acceptance. Perhaps 

 the most usual sense in which the term is 

 used is that in which it means the sum of 

 the digestible protein multiplied by a factor 

 (usually 1.94) plus the digestible fat multi- 

 plied by a factor (usually 2.3), plus the 

 digestible carbohydrates. This, however, 

 gives misleading values which are too high 

 in concentrated foods and too low in bulky 

 foods, the discrepancy being due to the 

 larger proportion of the energy of the 

 bulky foods which is used up in the much 

 greater work of digestion which they re- 

 quire. Kellner and his school have devised 

 a method which measures the starch equiva- 

 lent by experiment, a much more satis- 

 factory and practical method than any 

 system which depends purely on calcula- 

 tion. 



An animal or a number of animals are 

 kept on a maintenance diet so that their 

 weight remains constant. To this diet is 

 added a known weight of starch, and the 

 increase in weight observed. The animal 

 or animals are then placed again on the 

 same maintenance diet for some time, and 



