132 THE CHEMISTRY OF THE TISSUES AND ORGANS. 



The chief acid present throughout is phosphoric acid ; the chief base 

 in human rnilk is potash ; but this in most other mammals is second to 

 lime ; in dogs' milk the lime is especially high. 



In connection with the iron in the milk it is to be noticed, that 

 although the other mineral constituents of the milk are present in the 

 proportion in which they are contained in the foetal tissues, the quantity 

 of iron in milk is less. 



One hundred parts by weight of ash contain 



In New-born Dog. In Dogs' Milk. 



K 9 . . 11-42 . . 14-98 



Na 2 . . 10-64 . . 8-80 



CaO . . 29-52 . . 27*24 



MgO . . 1-82 . . 1-54 



Ee 2 (X . . 0-72 . . 0-12 



P 2 5 . . 39-42 . . 34-22 



Cl . 8-35 . . 16-90 



The slightly different proportion in soda and potash is easily ex- 

 plained by the fact that in the young animal the potash-rich muscle is 

 increasing, and the soda-rich cartilage is diminishing. The high per- 

 centage of chlorine in the milk is also explicable, on the hypothesis that 

 the chlorides serve not only to build up tissues, but also largely as 

 solvents in removing waste products. But the percentage of iron 

 in the milk is only one-sixth of that in the foetal tissues. The foetus 

 obtains its supply of iron before birth through the placenta, and stores 

 it in the liver (see p. 86). As the young animal grows, a kilogram of 

 body weight contains less and less iron. 



Iron appears to pass to the offspring through the placenta rather 

 than by the milk, because of the difficulties of absorbing iron by the 

 alimentary canal, and the danger that heematogenous (i.e. nuclein) 

 compounds may there become the prey of bacteria. Bunge further 

 regards it as probable that the large amount of iron which passes to the 

 foetus is not all derived from the mother's food during the relatively 

 short period of pregnancy, but that a storage of iron occurs in the 

 maternal organs even before the first conception ; and this may explain 

 the occurrence of chlorosis at the age of puberty. 



The carbohydrates of milk. The most important carbohydrate 

 in milk is lactose, or milk-sugar, the properties of which are described 

 on page 12. . It is found in varying quantities in the milk of all 

 animals ; the only exception to this rule hitherto noted is that of 

 the Egyptian buffalo (JBos bubalus), where it is replaced by another 

 sugar christened tewfikose 1 by Pappel and Richmond ; 2 it yields dex- 

 trose only on hydrolysis. 



Though lactose is not fermented by yeast, yet it undergoes the 

 alcoholic fermentation under the influence of other schizomycetes, as 

 in the preparation of koumiss and kephir. 



Ritthausen 3 found in milk another carbohydrate which is soluble in water, 

 and is not crystallisable ; its reducing power is low, and increased after boiling 



1 After the Khedive of Egypt. 



2 Journ. Chem. Soc., London, 1894, p. 754. 



3 Journ. f. prakt. Chem., Leipzig, N. F., Bd. xv. 



