* 
ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 97 
the average composition of various milks is Leach’s compilation from 
Koenig’s, ‘‘ Chemie der mensch-Nahrung und Genussmittel.” 
Constant. Cow, Human. Goat. Ewe. Mare. Ass. 
dee 10316 1:03 10305 10298 1:0347 1:036 
Water percent. 87°27 87°41 85°7) 80°82 90°78 89°64 
Casein. 3°02 1:03 3°20 4°37 1°24 0°67 
Albumen. 0°53 1°26 1:09 15A O75 1°55 
Fat. 3°64 378 478 6°86 1:21 164 
Milk Sugar. 4:88 6°21 4:46 4-91 5°67 5-99 
Ash. 071 O31 0°76 0°89 0°35 0°51 
lt has long been known that infants can digest human and asses’ 
milk more easily than cows’ milk cf. Jacobi, Jowrn. Am. Med. 
Assocn. 51, 1216-1219 (1908). ‘ Asses’ milk has always been recog- 
nised as a refuge in digestive disorders, when neither mothers’ or 
cows’ milk, or its mixtures, were tolerated.” 
From the above table we see that in cows’ milk the ratio of 
albumen to casein is only 0: od to 3°02, whereas in human milk it is 
1:26 to 1:03, and in agses’ milk 1°55 te 0°67 (or over double the 
amount). ‘In cows’ milk the casein forms 5/6ths of the total pro- 
teids in the milk, whereas in women’s milk the casein forms 2/6ths 
4 the total proteids.” (Koplik, “ Diseases of Infancy & Childhood,” 
1902.) 
Human milk is hardly curdled at all by acid or rennin, the 
reverse being true with cows’ milk. We see then, that the ratio of 
protective colloid (albumen) to the irreversible coagulative colloid 
(casein) is a most important factor. 
“ Cows’ milk pr ecipitates or coagulates very early with the aid of 
acids or salts; women’s milk quite late or not at all. Hence in the 
infant stomach, cows’ milk does not take up much acid of the gastric 
juice and soon coagulates in large masses. ._ Women’s milk, on the 
other hand, tales up a large amount of acid of the gastric juice, and 
coagulates late in small masses. The differences in the modes of 
coagulation in the two caseins are of great importance in the study of 
infant feeding.” (Koplik. loc. cit.) 
Cows’ milk can be made to resemble human or asses’ milk in 
protective qualities by the addition of such colloidal subtances as 
_ gelatine, gum-arabic, cereal gruel, or barley water (a starchy solution). 
Very interesting observations with the ultra-microscope were made 
_ by Alexander and Bullowa on this subject :—see Chem. News, 101, 
193 (1910). These authors followed the coagulation of milk by heat, 
rennin, and acids, with and without the addition of protective 
colloids, by the aid of the ultra-microscope. They concluded that 
“the casein of milk is an irreversible or coagulating or unstable 
colloid, which is protected by lact-albumen, a reversible or stable 
colloid,” and further that “in the modification of cows’ milk for 
infant feeding, it is necessary not only to consider the per cent. of 
total proteids, fat, etc., present but to see that the casein is adequately 
_ protected.” (Loe. cit., p. 195.) 
The fat present in milk is carried down by the curd resultant 
upon milk-curdling. Ihe greater the extent of coagulation, the 
larger is the amount of fat “carried down with the curd, and since 
¥ such fatty curds tend to coalesce and give rise to large masses little 
_ amenable to the action of the digestive juices, ‘it follows that 
20895 D 
