554 MANUAL OF HISTOLOGY. 



These globules (fig. 543, a), present the usual optical characters of oil drops, 

 and an average diameter of 0-0023-0-0090 mm. 'Under ordinary circum- 

 stances they do not coalesce, but do so readily on the addition of acetic acid, 

 showing that each particle possesses a very delicate 

 membrane of some protein substance, probably casein. 

 The microscopic appearance, however, of milk, 

 which is secreted in the last days of pregnancy, and 

 immediately after parturition, continuing sometimes, 

 even under abnormal conditions, for a longer period, 

 is quite different. This fluid is known as colostrum. 

 It is of strong alkaline reaction, rich in solid con- 

 stituents and salts, and contains, besides fatty globules, 



ther bodies to which the name f Colostrum COT- 



a, globules; 6, cuio- puscles has been given. These (b) are spherical struc- 

 tures of from 0-0151 to 0-0564 in diameter, consisting 

 of an agglomeration of oil globules, held together by some species of 

 cement. Sometimes a nucleus may be found in them, besides which 

 they are endowed with the power of contractility, sluggish no doubt, but 

 unmistakable (Strieker, Schwarz). 



Taking milk chemically, we find in it, besides water, casein (p. 17), 

 neutral fats (p. 26), and a kind of sugar known as sugar of milk (p. 33); 

 further, extractives and mineral constituents, free carbonic acid, and 

 nitrogen, gases, and small quantities of oxygen (Hoppe). Even blood and 

 bile pigments may also be abnormally present. 



Casern is generally supposed to occur partly in combination with soda, 

 dissolved in the watery portion of the milk, and partly, as we have already 

 remarked, coagulated in the form of delicate membranes around the milk- 

 globules. The amount of phosphate of calcium present in this fluid is 

 quite remarkable. Albumen also appears to exist in milk, but in colos- 

 trum it is undoubtedly present. The neutral fats of the milk consist 

 first of the ordinary fatty matters, and then of those which, on saponifi- 

 cation, set free butyric, capronic, caprylic, and capinic acids (p. 25). 

 We have already spoken of them in detail in an earlier section. The 

 sugar of milk is found in solution, as also the extractives and the majority 

 of the mineral ingredients. The latter consist of chlorides of sodium and 

 potasium, of combinations of phosphoric acid with the alkalies and earths, 

 and of soda and potash with casein ; iron is also present. The insoluble 

 salts usually preponderate. 



The name "fairy's milk" (Hexenmilch) has been applied to a peculiar 

 milky secretion produced by the mammary glands of infants for some 

 days after birth. 



In the quantitive analysis of human milk we must bear in mind that it 

 varies considerably according to age of the individual, and nature of food 

 indulged in by the latter. These variations are much more decidedly 

 marked in many of the mammalia. The following is an analysis of 

 Simon's : 



1000 parts contain 



Water, 880-6 



Casein, 37 -0 



Sugar of milk, 45*4 



Fatty matters, . . . . . 34-0 

 Extractives and salts, . . . . 3'0 



