1 32 THE CHEMISTRY OF THE TISSUES AND ORGANS. 
The chief acid present throughout is phosphoric acid ; the chief base 
in human milk 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.,0 
11-42 
14-98 
Na 2 
10-64 
8-80 
CaO 
29-52 
27-24 
MgO 
1-82 
1-54 
Fe 2 < >.. 
0-72 
0-12 
PA 
39-42 
34-22 
CI . 
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 hsematogenous (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 (Bos bubalus), where it is replaced by another 
sugar christened tewfikose 1 by Pappel and Bichmond; 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. 
Bitthausen 3 found in milk another carbohydrate which is soluble in water, 
and is not crystallisable ; its reducing poAver is low, and increased after boiling 
1 After the Khedive of Egypt. 
2 Journ. Chem. Sue, London, 1894, p. 754. 
3 Journ. f. prakt. Chem., Leipzig, N. F., Bd. xv. 
