658 
cent of proteid to 1.50 per cent in woman’s milk. The reason for this 
difference is obvious. As all growth is dependent upon proteid ma- 
terial, and animals are unable to build up proteids within themselves 
from the nonnitrogenous portions of their diet, they are dependent 
for their supply upon the ingestion of proteid in their food. As the 
ratio of growth of the calf compared to the infant is about as 2 is to 1, 
it follows that the calf requires relative^ twice as much proteid as 
does the infant. Moreover, owing to differences in their respective 
digestive tracts^the proteid in cow’s milk is of a different composition 
from that of woman’s milk. In the human being the stomach forms 
20 per cent of the intestinal tube and digestion is chiefly intestinal. 
In the cow the stomach forms TO per cent of the digestive tract and 
digestion is chiefly gastric. Under the action of the active rennet 
ferment present in the stomach of the calf, cow’s milk forms a large 
curd which remains in the calf’s stomach until digestion is complete. 
In the infant the soft, flocculent curd of mother’s milk is adapted 
to easy transit from the stomach to the duodenum, and it is alto- 
gether likely that a portion of the milk ingested does so pass out be- 
fore the nursing is finished. 
In view of the foregoing, as casein is the curding proteid in milks, 
we should expect to find, as is actually the case, that the proteid of 
cow’s milk is richer in casein than the proteid of human milk. Koenig 
gives the following composition of the proteids in cow’s milk and 
human milk : 
Lactal- 
bumen. 
Casein. 
Human milk _ __ . 
Cow’s milk 
Per cent. 
1.26 
.53 
Per cent. 
1.03 
3.02 
The proteid of cow’s milk when coagulated by rennet in the test- 
tube gave 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 every 
bit as fine as the curd of human milk. This statement Heubner con- 
firmed 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- 
