THE SECRETION OF MILK IN THE UDDER. 37 



Nuclein, lecithin, and cholesterin were found to be abundantly present 

 in the colostrum. The sugar found was not milk-sugar, but a sugar capable 

 of direct alcoholic fermentation; and the fat possessed a melting point of 

 between 40 and 44, which is a very high melting point. 



An analysis of ten samples of colostrum, made in the author's labora- 

 tory, showed in all cases comparatively large quantities of cholesterin and 

 lecithin. Leucin, tyrosin, urea, animal gum, and in some cases peptones 

 were also found. In the ether extract were found fat and small quan- 

 tities of free fatty acids and a yellow colouring matter. In addition to 

 milk-sugar, grape-sugar was found, and perhaps also some other kind of 

 sugar. Finally, the ash was found to be richer in the alkaline earths and 

 in phosphoric acid, and poorer in alkalies, than the ash of milk. 



13. The Secretion of Milk in the Udder. The physiological 

 forces at work in the milk-glands, during the period of lactation, are 

 dependent on the special surroundings of the individual animal and 

 on its condition. They give rise not merely to an active up-building 

 of tissue, but they also drive the secreted fluid into the cavities of 

 the glands and udder, and work without any external opposition 

 so long as tbe udder is not full. As soon as the cavity of the udder 

 is full, however, and when, owing to the continuous accumulation 

 of the quantity of the secretion, it begins to distend, there arises an 

 ever-increasing pressure against the sides of the secreting glands, 

 which most probably does not continue without a weakening reflex 

 action on the physiological forces above referred to. Perhaps this 

 explains the fact, found by experience, that the more frequently an 

 animal is milked in a day, it yields so much the more milk, contain- 

 ing a larger percentage of solids. It has also been found that the 

 quantity of milk obtained is in direct proportion to the percentage 

 of dry matter in the milk, but in inverse proportion to the length 

 of time between the successive milkings. The fact often observed 

 in practice, that milk, when yielded in large quantity, contains less, 

 and in small quantity more, dry substance, may be partly attributed 

 to the action and reaction of pressure. Generally, however, these 

 phenomena are due to other causes. The question as to whether 

 the milk lies in a ready-formed condition in the udder, or whether a 

 part is formed through the excitation of the nerves connected with 

 the milk-secreting organs during milking, in consequence of the 

 withdrawal of pressure in the udder, must be regarded as an open 

 one. The experiments made on this subject bave given no decisive 

 results. 



