4G4 MILK AND ITS PREPARATIONS. 



ulation of the sensory nerves of the nipple. The vessels of the gland are dilated, 

 and there is a copious transudation into the gland, the transuded fluid being 

 manufactured into milk under the influence of the secretory protoplasm. The 

 amount of secretion depends upon the blood-pressure (Rohrig). During sucking, 

 not only is the milk in the gland extracted, but new milk is formed, owing to the 

 accelerated secretion. Emotional disturbances anger, fear, &c. arrest the secre- 

 tion. Laffont found that stimulation of the mammary nerve (bitch) caused 

 erection of the teat, dilatation of the vessels, and secretion of milk. After section 

 of the cerebro-spinal nerves going to the mamma, Eckhard observed that erection 

 of the teat ceased, although the secretion of milk in a goat was not interrupted. 

 The rarely observed galactorrh(Ea is perhaps to be regarded as a paralytic secre- 

 tion analogous to the paralytic secretion of saliva. Heidenhain and Partsch found 

 that the secretion (bitch) was increased by injecting strychnine or curara after 

 section of the nerves of the gland. The "milk-fever," which accompanies the 

 first secretion of milk, probably depends on stimulation of the vaso-motor nerves, 

 but this condition must be studied in relation with the other changes which 

 occur within the pelvic cavity after birth. [Some substances, such as atropin, 

 arrest the secretion of milk.] 



231, Milk and its Preparations. 



Milk represents a complete or typical food in which all the con- 

 stituents necessary for maintaining the life and growth of the body 

 are present. To every 10 parts of proteids there are 10 parts fat and 

 20 parts sugar. Eelatively more fat than albumin is absorbed from 

 the milk (Rubner) ; while a part of both is excreted in the faeces. 



Characters. Milk is an opaque, bluish-white fluid with a sweetish 

 taste and a characteristic odour, probably due to the peculiar volatile 

 substances derived from the cutaneous secretions of the glands, and 

 it has a specific gravity of 1026-1035 (Radenhausen). When it 

 stands for a time, numerous milk-globules, butter-globules, or cream, 

 collect on its surface, under which there is a watery bluish fluid. 

 Human milk is always alkaline, cow's milk may be alkaline, acid or 

 amphoteric ; while the milk of carnivora is always acid. 



Milk-Globules. When milk is examined microscopically, it is seen 

 to contain numerous small highly refractive oil-globules, floating in a 

 clear fluid the milk-plasma (Fig. 172, a, &,); while colostrum-corpuscles 

 and epithelium from the milk-ducts are not so numerous. The white 

 colour and opacity of the milk are due to the presence of the milk- 

 globules which reflect the light ; the globules consist of a fat, or butter, 

 surrounded with a very thin envelope of casein. If acetic acid be 

 added to a microscopic preparation of milk, this caseous envelope 

 is dissolved, the fatty granules are liberated, and they run 

 together to form irregular masses. If cow's milk be shaken with 

 caustic potash, the casein envelopes are dissolved, and if ether be 

 added, the milk becomes clear and transparent, as the ether dissolves 



