38 Thomson on the Food of Jinimals, 
THOMSON ON THE FOOD OF ANIMALS- 
The importance of the subject to which this work relates can- 
not easily be over-estimated. A more accurate knowledge than 
we now possess of the modes in which different kinds of food are 
affected by the digestive process, the readiness with which they 
are assimilated to the system, and consequently their capacity as 
to the power of nutrition, would be of the greatest practical utili- 
ity, and would probably lead us to modify the dietary treatment 
of nearly all our domesticated animals. Yet it is surprising how 
little has been done, still more so, how little has even been at- 
tempted, to throw light on this important matter. In this, as in 
most other branches of his avocation, the farmer has to be guided 
by the results of experience, obliged to depend on a kind of em- 
pirical knowledge, and be satisfied with certain effects, without 
well knowing how these are produced; and, consequently, with- 
out much power of modifying them, or giving them such a direc- 
tion as might most effectually promote his interests. It must be 
admitted that the subject is encompassed with difficulties. The 
whole process of digestion and nutrition is exceedingly complex, 
obscure in its own nature, and carried on in regions of the sys- 
tem nearly or altogether inaccessible to observation. Even were 
we acquainted with the whole chemistry and mechanism of the 
subject, able to assign their due office and proportion to all the 
acids, alkalis, gases, &c., which take a share in the process, we 
should still be very far from having a perfect understanding of it. 
The nervous action — the general influence of the vital principle 
— are obviously agents of the first importance, and are so myste- 
rious in their operations, that w^e can scarcely hope to get into 
the secret of their modes of action. But while there may be 
much, as in the analogous phenomena of generation, which is 
likely even to bid defiance to our scrutiny, not a little remains on 
which much light may be thrown, and much practical information 
elicited, by a series of judicious, ingenious, and enlightened ex- 
periments. 
Such, we have no hesitation in affirming, is the character of 
the experiments recorded in this little volume. Dr. Thomson is 
well qualified for such an undertaking, not only by his knowledge 
of chemistry, but by his skill as a physician, and habitual ac- 
quaintance with the habits and characters of animals. The ex- 
periments in question were undertaken at the instance of the late 
government. The original object of the inquiry was to determine 
the relative influence of barley and malt in feeding cattle; but ad- 
vantage was taken of the opportunity to investigate some scien- 
tific problems of great importance to physiology, and of extreme 
value in the physical management of man and animals. 
