332 MILK. 



necessary, since the former pertains to purely physical physiology, 

 arid the latter are altogether beyond the domain of scientific 

 investigation. 



MILK. 



This glandular secretion, which is peculiar to the mammalia, 

 is generally of a white, but frequently of a bluish-white colour, 

 more rarely of a somewhat yellowish tinge, opaque, without odour, 

 of a slightly sweet taste, and an alkaline reaction. Its specific 

 gravity fluctuates, according to Scherer,* between 1*018 and 1*045, 

 but in women is on an average 1*032 (Simon). 



As is well known, milk, when allowed to stand for some time, 

 exhibits on its surface a thick, fatty, yellowish white stratum, the 

 cream, while the fluid below has become poorer in fat, and has, 

 therefore, a greater specific gravity than fresh milk, and has likewise 

 a more bluish white colour. When milk stands in a not very low 

 temperature, it gradually begins to exhibit an acid reaction, 

 remaining for some time thinly fluid, more especially after it has 

 been repeatedly boiled. But if it has not been boiled, and the 

 temperature be somewhat above the mean, and if there should be 

 considerable electrical tension in the atmosphere, the acid will 

 increase to so great a degree that the casein of the milk will be 

 precipitated ; that is to say, the milk will coagulate, become thick, 

 and gradually be converted into a moderately thick pulp. The 

 milk may be made to coagulate artificially by rennet, both when 

 it has an acid as well as an alkaline reaction (see vol. i., p. 375). 

 When exposed to rapid evaporation, milk becomes coated with a 

 dense white membrane. 



It would, of course, be superfluous to make any remarks as to 

 the mode of procuring animal milk ; it must, however, be observed, 

 that it frequently is extremely difficult to obtain any considerable 

 quantity of milk from women who are suckling. We need not, 

 however, enumerate any of the well-known manipulations and 

 methods, which are familiar to every practitioner, for procuring a 

 sufficient quantity of milk to serve for a physical examination. 

 The special forms of apparatus employed for this purpose are 

 almost all based upon the principle of rarefaction or suction, but 



* Handworterb. der Physiol. Bd. 2, S. 449475. 



