MILK AND ITS PREPAEATIONS. 



345 



centre of the gland, while the connective-tissue at the same time becomes somewhat more 

 opened out. At the climacteric period, or menopause, all the acini and numerous fine milk- 

 ducts degenerate. In the adult male, the gland remains in the.non -developed infantile condition. 

 Accessory or supernumerary glands upon the breast and abdomen are not uncommon, sometimes 

 the mamma occurs in the axilla, on the back, over the acromion process, or on the leg. A 

 slight secretion of milk in a newly-born infant is normal. 



During the evacuation of the milk (500-1500 cubic centimetres daily), there is not only the 

 mechanical action of sucking, but also the activity of the gland itself ( 152). This consists in 

 the erection of the nipple, whereby its non -striped muscular fibres compress the sinuses on the 

 milk-ducts, and empty them, so that the milk may flow out in streams. The gland acini are 

 also excited to secretion reflexly by the stimulation 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 secretion. 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 galactorrhcea is perhaps to be regarded as a paralytic secretion analogous to the 

 paralytic secretion of saliva. Heidenhain and Pratsch 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 are present all the constituents necessary for maintaining 

 the life and growth of the body of an infant ( 236). [If an adult were to live on 

 milk alone, to get the 23 oz. of dry solids necessary, he would have to take 9 pints 

 of milk daily, which would give far too much water, fat, and proteids.] To every 

 10 parts of proteids there are 10 parts fat and 20 parts sugar. Eelatively more 

 of the fat than the albumin of the milk is absorbed (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 to 1035. 

 When it stands for a time, numerous milk 

 globules, butter globules, or cream, collect 

 on its surface, under which there is a bluish 

 watery fluid. Human milk is always alka- 

 line, 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 (figs. 234, 

 a, b, 235) j 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 i^\SS^Sm^iM half^" 

 consist of a fat, or butter, and are said by 

 some to be surrounded with a very thin envelope of casein or haptogen membrane. 



If acetic acid be added to a microscopic preparation of milk, the fatty granules run together 

 to form irregular masses. If cow's milk be shaken with caustic potash, the casein envelopes 



Fig. 235. 



