717 
Lactal- 
bumen. 
Casein. 
Human milk 
Per cent. 
1.26 
.53 
Per cent. 
1.03 
3.02 
Cow’s milk - 
The proteicl of cow’s milk when coagulated by rennet in the test- 
tube gives a firm, tough, contractile curd. Heubner, however, has 
shown that we can by no means infer that this is the action in the 
human stomach ; for, if rennet is added to cow’s milk in a test tube, 
the tube subsequently corked, and then slowly turned over end for 
end to imitate the movements of peristalsis, the resulting curd is 
ever}^ bit as fine as the curd of human milk. This statement Heubner 
confirmed by withdrawing cow’s milk shortly after ingestion by 
infants with a stomach tube. 
This brings us to the consideration of a fact due to the researches 
of Heubner, Keller, and Czerny, which tends to revolutionize all 
our preconceived notions on this side of the Atlantic at least as to the 
digestibility of cow’s milk proteid. For many years it has been held 
that the proteids of cow’s milk are very difficult of digestion. To 
overcome this supposed difficulty very many devices have been advo- 
cated. Thus various alkalies and diluents have been applied, the 
percentage of proteids has by modification been attenuated almost to 
the vanishing point, split proteids have been advocated, a portion of 
the casein being replaced by whey proteid — in short, almost every 
conceivable device that ingenuity could suggest. 
This would be highly commendable were cow’s milk proteid really 
so difficult of digestion by the human infant. The researches of the 
investigators just adverted to have shown this important fact, viz, 
that cow’s milk proteid is almost as easily digestible per se by infants 
as are the proteids of woman’s milk. In this country Brennemann 
and Walls have eonfimed this view. On the other hand, Czerny 
and Keller have shown that the element in cow’s milk which causes 
digestive disturbance is the fat and not the proteid. They have given 
us a very precise and definite clinical picture of these disturbances, 
a picture perfectly familiar to all who have dealt much with the 
artificial feeding of infants, but which has been ascribed heretofore 
in this country to difficult proteid digestion. 
Let us then examine the basis for this belief which has hitherto 
been regarded as a fundamental fact ever to be considered in the 
percentage system of the modification of cow’s milk. It has been 
based for the most part on these facts: First, that in the stools fol- 
°Am. Journal Med. Ass., 1907, Vol. XLVI1I, 1338—1844; Ibid., F. X. Walls, 
pp. 1389 to 1392. 
