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 
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- 
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- 
tioners that there is a very distinctly lowered vitality among infants 
which are fed on boiled milk, the process of absorption being. delayed 
and the quantity of milk required for the nourishment of the child 
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 
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 
even a short heating at 100° C. coagulates the lactalbumin, an obser- 
vation which has been confirmed by Middleton (58). De Jager (59) 
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 Lbrcher (60) that 
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 
6? 
60 
4^ 
90 
8§ 
70 
4| 
100 
9i 
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 
