880 Physiology of the Domesticated Animals. 
through digestion, is rendered capable of absorption and does actually 
enter the blood, in proportion to the amount which remains un- 
digested, or which is not so absorbed. This percentage is known 
as the co-efficient of digestion, and varies according to the composi- 
tion of the food and to the mode of digestion of different classes of 
animals. The principles thus briefly enunciated are well illustrated 
by numerous examples, drawn from farm animals and their food. 
Before the food, which is the basis of nutrition, can become really 
serviceable in the nourishment of the higher animals, its ingredients 
must become incorporated with, and submitted to the action of, 
the blood. Absorption is the means whereby nutritive and other 
matters enter the blood ; digestion is the preparation of the food for 
absorption, and different modes of such preparation are respectively 
necessary for albuminoids, for carbo-hydrates, and for fats. The blood 
is the medium whereby the various parts of the body are nourished, for 
by means of its circulation it is the carrier to and from all the organs. 
An interesting section of the work is included in the twenty- 
six pages dealing with the mammary secretion. The respective 
origins of the fat, the casein, and the sugar of the blood are discussed 
at some length. The author regards the secretion of milk ' as a 
process of moulting ' of the epithelial cells of the mammary gland, 
which undergo decomposition, and discharge the resulting products 
into the excretory ducts. 
The food required by horses, cattle, sheep, and swine under 
different conditions is shown by means of numerical tables indicating 
for every kilogramme of body-weight the quantities of the digestible 
food-stuffs which should be contained in the daily ration. As regards 
the duration of the interval between meals, too frequent feeding is 
discountenanced, as it would shorten the pauses which are necessary 
between the digestive processes. On the other hand, if the intervals 
between feeding be too long, the great increase of hunger which 
results leads to faulty mastication, and imperfect insalivation of the 
food. 
The chapter on the physiology of movement will be studied with 
much interest by all who would rightly understand the mechanisms 
which underlie what is termed ' action ' in the horse. The subject 
is made the more attractive by the reproduction of Colin's illustrations 
portraying the oscillations of the limbs, and of Muybridge's plates 
showing the successive movements which respectively enter into walk- 
ing, ambling, pacing, trotting, cantering, and running. Another 
apt illustration shows the resultant of the propelling forces which 
are called into play when a horse is hauling from the collar. 
The physiology of the nervous system is less thoroughly treated 
than might have been expected — that is, in so far as the domesti- 
cated animals are concerned. There may be noticed a tendency, on 
the one hand, to branch off into psychological details, and, on the 
other, to tacitly assume that certain facts pertaining to man are equally 
applicable to farm animals. But, granting the difficulties with which 
the study of nerve functions is surrounded, there can be little 
excuse for giving one anatomical description of the eye as serving 
