~ and always will be, most useful. 
OcTOBER 30, 1913| 
Thus, for instance, 
Bombay cotton cake, when first put on the market, 
was thought to be dangerous on account of its woolly 
appearance. It was tried, however, by several of the 
agricultural colleges and found to be quite harmless to 
cattle. Its composition is practically the same as 
that of Egyptian cotton cake, and it now makes on 
the market practically the same price. 
Soya-bean cake is another instance of a new food 
which has been similarly tested, and found to be safe 
for cattle if used in rather small quantities and mixed 
with cotton cake. The price is now rapidly rising to 
that indicated by its analysis. Work of this kind is, 
Trials with few 
animals, whilst they cannot measure accurately the 
feeding value of a new food, are quite good enough to 
demonstrate its general properties, and its price will 
then gradually settle itself as the food gets known. 
Turning to the more strictly scientific aspects of 
animal nutrition, entirely new ideas have arisen during 
the last twenty years. I propose to discuss these 
shortly, beginning with the proteins. Twenty years 
ago the generally accepted view of the réle of 
proteins in nutrition was that the proteins in- 
gested were transformed in the stomach and gut 
into peptones, and absorbed as such without further 
change. Splitting into crystalline products, such as 
leucin and tyrosin, was thought only to tale place 
when the supply of ingested protein exceeded the 
demand, and peptones remained in the gut for some 
time unabsorbed. It is now generally agreed that 
ingested protein is normally split into crystalline pro- 
ducts which are separately absorbed from the gut, and 
built up again into the various proteins required by 
the animal. If the ingested protein does not yield a 
mixture of crystalline products in the right propor- 
tions to build up the proteins required, those crystalline 
products which are in excess are further changed and 
excreted. If the mixture contains none of one of the 
products required by the animal, then life cannot be 
maintained. This has been actually demonstrated in 
the case of zein, one of the proteins of maize, which 
contains no tryptophane. The addition of a trace of 
tryptophane to a diet, in which zein was the only 
protein, markedly increased the survival period of 
mice. 
The adoption of this view emphasises the importance 
of a knowledge of the composition of the proteins, 
and especially of a quantitative knowledge of their 
splitting products, and much work is being directed 
to this subject in Germany, in America, and more 
recently in Cambridge as a result of the creation there 
of an institute for research in animal nutrition by the 
Board of Agriculture and the Development Commis- 
sion. This work is expected ultimately to provide a 
scientific basis for the compounding of rations, the 
idea being to combine foods the proteins of which 
are, so to speak, complementary to each other, one 
giving on digestion much of the products of which 
the other gives little. Meantime, it is desirable that 
information should be collected as to mixtures of foods 
which are particularly successful or the reverse. 
Here the question. arises, for what purpose does the 
animal require a peculiarly complicated substance like 
tryptophane? The natural suggestion seems to be 
that the tryptophane grouping is required for the 
building up of animal proteins. It has also been sug- 
gested that such substances are required for the 
formation of hormones, the active principles of the 
internal secretions the importance of which in the 
animal economy has received such ample demonstra- 
tion in recent years. The importance of even mere 
traces of various substances in the animal economy 
is another quite recent conception. Thus it has been 
NO. 2296, VOL. 92] 
NATURE 
283 
feeding trials and found to be safe or otherwise, a | shown, both in Cambridge and in America, that young 
‘piece of most useful information. 
animals fail to grow on a diet of carefully purified 
casein, starch, fat, and ash, although they will remain 
alive for long periods. In animals on such a diet, 
however, normal growth is at once started by the 
addition of a few drops of milk or meat juice, or a 
trace of yeast, or other fresh animal or vegetable 
matter. The amount added is far too small to affect 
the actual nutritive value of the diet. Its effect can 
only be due to the presence of a trace of some sub- 
stance which acts, so to speak, as the hormone of 
growth. The search for such a substance is now 
being actively prosecuted. Its discovery will be of 
the greatest scientific and practical interest. 
Evidently new ideas are not lacking amongst those 
who are engaged in investigating the réle 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 conditions. It is obviously im- 
possible to fix this amount with any great accuracy, 
since proteins 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 containing about one pound of protein 
per 1000 lb. live-weight per day. All the British ex- 
periments of a more practical nature have been re- 
calculated on a systematic basis by Ingle, and tabulated 
in the Journal of the Highland and Agricultural 
Society. From them it appears that increase of pro- 
tein in the ration, beyond somewhere between one and 
a half and two pounds per tooo |b. live-weight per 
day of digestible protein, ceases to have any direct 
influence on increase in live-weight. 
We may fairly conclude, then, that about two ° 
pounds of proteins per tooo lb. live-weight per day is 
sufficient for a fattening ox. This amount is re- 
peatedly exceeded in most of the districts where beef 
production 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 
experiment and modern accountancy is required. 
Protein is the most expensive constituent of an 
animal’s dietary. If the scientific investigator, 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 1000 lb. live-weight per day for various 
types of animals, a great step will have been made 
towards making mutton and beef production profitable 
apart from corn-growing. 
For many years it has been recognised that an 
animal requires not only so much protein per day, 
but a certain quota 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 equivalent. 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 94) plus the digestible fat multivlied 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 pro- 
portion of the energy of the bulky foods which is 
used up in the much greater work of digestion which 
