332 
slightly alkaline solution than in acid solution. Acidity and tem- 
perature naturally augment the destructive powers of each other 
toward the enzymes. This accounts for the apparent discrepancies 
existing among such observations. In general it may be said, how- 
ever, that the milk ferments, most of them at least, can withstand a 
temperature ranging from 60°-65° C. for some time, without mate- 
rial injury. Between 65° C. and 70° C. most of them are weakened 
in their activities, and between 70° G. and 80° C. all of them are 
destroyed, even after relatively short exposures. 
According to Raudnitz (47) all the ferments of milk are destroyed 
between 75° C. and 90° C. (See also Tjaden, Koske, and Hertel (48), 
and also E. Weber (49), for further information bearing on this 
point.) 
The digestibility of raw and heated milk . — In this connection the 
effect of heat'on the digestibility of milk proteids has been the sub- 
ject of considerable investigation. According to Kerr (50) milk is to 
be looked upon as consisting of living cells suspended in serum, the 
former consisting of fat cells and nucleated cells of the nature of 
white blood corpuscles. (As a matter of fact it has been definitely 
proven that leucocytes do actually occur in milk — see p. 477.) Ac- 
cording to Kerr, when milk is ingested, these living elements are at 
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 (51) the milk proteids are rendered somewhat more difficult of 
digestion as the result of heating. Rubner (51a) has observed that 
even a short heating at 100° G. coagulates the lactalbumin, an obser- 
vation which has been confirmed by Middleton (51b). De Jager (52) 
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 (53) that 
cooked milk coagulates with rennin more slowly than uncooked milk. 
