SECRETARY'S REPORT. 39 



elaborate from the blood certain products, which are destined 

 for special uses in the economy, than to eliminate matters 

 wliose retention in the circulating current would be injurious." 

 These glands, called mammary glands, perform as is supposed 

 tiie chief part of the work of elaborating the elements of 

 milk ; although it is not yet ascertained how much of this 

 elaboration takes place in the blood during its circulation. Be 

 this as it may, the production of milk is a very different busi- 

 ness from the production of fat, and does not result in the 

 combination of the same elements, as are contained in the 

 ^dipose tissue and fat-cells. 



It is well known, moreover, that the proportion of two, at 

 least, of the principal ingredients of milk, is lial)le to great 

 variation with the circumstances of the animal. Dr. Playfair 

 has ascertained " that the proportion of butter depends in part 

 upon the quantity of oily matter in the food ; and in part upon 

 the amount of exercise which the animal takes, and the warmth 

 of atmosphere in which it is kept. Exercise and cold, by 

 increasing the respiration, eliminate part of the oily matter in 

 the form of carbonic acid and water ; while rest and warmth, 

 by diminishing this drain, favor its passage into the milk. 

 The proportion of casein, on the other hand, is increased by 

 exercise ; which would seem to show that this ingredient is 

 derived from the disintegration of muscular tissue." The 

 experience of every farmer teaches him that an animal which 

 has a large, heavy, muscular development, and is thus furnished 

 with the means of rapid locomotion, is seldom a good milker. 

 Her digestive apparatus is more devoted to her fleshy fibre 

 than to the preparation of milk. The same may be said of fot 

 and bone. So true is this, that among cattle bred expressly for 

 the stall, the females often furnish hardly milk enough to 

 sustain their own offspring ; and in countries where the bone 

 and muscle of the cow are developed by labor, her service in 

 the dairy amounts to but little. 



It would seem, therefore, that in rearing animals for the 

 dairy, care should be taken that the young are not so fed as 

 to develop a tendency to great size, either in frame or in 

 adipose tissue ; nor so as to establish in the end a race which 

 has every faculty except that of producing milk. We bave all 

 seen how high-feeding of the young has in a few generations, 



