294 THE COMPLETE GRAZIER. BOOK n. 



identified by chemists, than upon the fixed oils which compose it. 

 Nevertheless, these principles, as well as those which determine the 

 colour of butter, are unquestionably influenced by food and treatment. 

 The question remains, How ? 



When cows are largely fed on watery herbage, brewers' grains, or 

 other food containing a high percentage of water, the milk becomes 

 poorer in solids, or, in other words, the proportion of water in the milk 

 increases. This probably arises from the more watery, or poorer, 

 character of the blood, for water taken into the stomach is absorbed 

 almost immediately by the blood capillaries and lymphatics in the walls 

 of that organ, as is proved by the instant alleviation of thirst when water 

 is drunk. A course of poor watery diet, then, impoverishes the blood, 

 and poor blood leads to the production of poor milk in the mammary 

 gland of milk, that is, which contains a larger percentage of water 

 than would be the case with better food. 



Both the secretion and the excretion of milk are under the control of 

 the nervous system, but the exact mode whereby the nervous influence 

 is exerted remains to be worked out. Indirectly, however, the secretion 

 of milk must be largely affected through the sympathetic nervous 

 system, whose centre is in a chain of nervous elements extending along 

 the general body cavity just beneath the backbone. This system is 

 distinct from, though connected with, the brain and spinal cord, and it 

 largely contributes to, amongst others, the vase-motor nerves. These 

 nerves are so called because they are connected with the muscular 

 walls of the blood vessels, and, through their influence on the vascular 

 muscles, determine whether the calibre of the vessels shall be increased 

 or diminished ; through them, therefore, the quantity of blood which 

 flows along an artery in a given time is regulated. Thus, undue 

 exposure to cold produces an effect on the skin which is conveyed to 

 the nervous centres, the vaso-motor nerves consequently experience a 

 partial paralysis, and are therefore incompetent to control the arterial 

 muscles in one or more organs of the body. The arteries lose their 

 normal tone, more blood passes through them than is compatible with 

 health, that undue distension of the blood vessels known as congestion 

 is set up, and inflammation is the usual result. It may not be the 

 mammary gland, but the lungs or intestines, which are the direct 

 sufferers, nevertheless, the mammary gland is bound to show the effects 

 of such adverse influences in its smaller and poorer secretions. And it 

 is not unlikely that a similar result is more directly produced when 

 undue stimulation of the vaso-motor nerves which control the arteries 

 of the mammary gland leads to an abnormal constriction of these vessels, 

 and so reduces the supply of blood to the secreting cells. In the case 

 of the kidney, indeed, it has been proved, that any irritation of the 

 nerves which control the muscular walls of the blood vessels supplying 

 the organ has the immediate effect of stopping the excretion of urine. 

 But the sympathetic nerves are further of interest in being those 

 through which an} T unkind treatment of the cow, wilful or otherwise, is 

 bound to show its effect in diminished yields of milk. Ill ventilated, 

 badly drained, or too draughty cow-houses, careless exposure to bad 



