339 
once absorbed without any preliminary digestion, and are utilized 
directly in the building up of the tissues. The effect of boiling there- 
fore is obviously to kill all of the living cells of the milk, and to coagu- 
late certain of the albuminoid constituents. The result of the boiling 
I therefore is that all of the constituents of the milk must be digested 
] before they can be absorbed into the system. Hence there is a dis- 
i tinct loss of utility in the milk as the result of boiling. He goes on 
to say further that, it has been observed by many medical practi- 
| !j tioners that there is a very distinctly lowered vitality among infants 
I which are fed on boiled milk, the process of absorption being delayed 
t and the quantity of milk required for the nourishment of the child 
I being greater than when fresh milk is used. 
^ While this is doubtless an extreme view to take of the matter, there 
are quite a number of observers who believe that the proteids of milk 
I are considerably altered by boiling. Thus according to Hallibur- 
ton (56) the milk proteids are rendered somewhat more difficult of 
digestion as the result of heating. Rubner (57) has observed that 
j,. even a short heating at 100° C. coagulates the lactalbumin, an obser- 
i vation which has been confirmed by Middleton (58). De Jager (59) 
I has also arrived at the conclusion that the digestibility of milk dimin- 
^ ishes with cooking, and also that caseinogen is more readily digestible 
» than casein and that infants stand raw milk better than cooked. 
£ In this connection it has been observed by Lorcher (60) that 
I cooked milk coagulates with rennin more slowly than uncooked milk. 
This effect is noted even at temperatures of 80°-90° C. This is 
shown by the following: 
Ten cubic centimeters of milk was heated to the following tem- 
peratures for five minutes, then cooled to 35° C., and 0.5 cubic centi- 
meter of rennin solution added, and the time required for coagulation 
noted. The following results were obtained : 
Temperature (°C.). 
Time re- 
quired for 
coagulation 
(minutes). 
Temperature (°C.). 
Time re- 
quired for 
coagulation 
(minutes). 
50 
4^ 
80 
65 
60 
41 
90 
85 
70 
4^ 
100 
9i 
1 
The probable explanation of the retardation of the rennin coagula- 
tion resulting from the heating of milk is that the calcium salts are 
partly rendered insoluble, probably through conversion into trical- 
cium phosphate, so that even the mineral constituents of milk seem 
to be somewhat altered by boiling. 
On the other hand there are those, among them Forbes-Ross (61), 
who contend that heat exerts no deleterious effect on the digestibility 
of milk, and that the feeding of infants with boiled milk is not in 
