329 
’ albuminous solution containing fat or paraffin. Rettger (5) also 
has arrived at the conclusion that its formation is dependent on the 
presence of proteid. This proteid is caseinogen. Surface evapora- 
tion and the presence of fat facilitate its formation although neither 
I is absolutely essential. According to Harris (6), also, the scum of 
i boiling milk consists very largely of caseinogen. It is also well 
known that certain changes occur in the odor and taste of milk as 
' the result of boiling. These changes seem to be due to the partial 
decomposition of certain of the proteids with the liberation of a 
; volatile sulphide, probably hydrogen sulphide. That such is the case 
; has been proven by Rettger (7) , and also by Franz Utz (8) . Accord- 
ing to the former, when milk is heated to 85° C., a volatile substance, 
; probably hydrogen sulphide, is liberated. The amount of this, 
‘ though small, suffices to blacken lead acetate paper and to decolorize 
I dilute solutions of potassium permanganate. He found that alkalis 
f and alkali phosphates accelerate the formation of the sulphide, 
I whereas acids and acid phosphates retard this change. According 
i to this author this change is believed to indicate proteid decomposi- 
I tion, and may partl}^ account for what some observers describe as 
II the injurious effect of heating milk. These observations have been 
j confirmed by Utz (8), who was able to recognize the hydrogen 
J sulphide resulting from the boiling of milk by lead acetate paper 
I and also by Ganassini’s reagent 
lAhen milk is boiled there seems also to be a partial fixation of the 
calcium salts which it ordinarily contains. These are probably par- 
tially precipitated in the form of tricalcium phosphate. This would 
account for the fact that the coagulation of milk by rennin takes 
place more slowly in boiled milk than in unboiled milk. (See p. 332.) 
In this connection Wassermann and Schiitze (9) have pointed out 
that cooked milk is not coagulated by lactoserum. According to 
P. T. Muller (10) the fact that cooked milk can not be coagulated by 
lactoserum is in some way associated with a diminution in the quan- 
tity of soluble calcium salts contained in the milk, this diminution 
having been caused by the action of heat. On the other hand, both 
Moro and Miiller (10) have observed that certain milks do not show 
any diminution in coagulability by lactoserum after boiling. Ac- 
cording to Miiller (10) this is to be attributed to the large amount 
of soluble calcium salts present in the milk of certain particular 
localities, and in this connection he has observed that the coagula- 
bility by lactoserum may be restored to boiled milk by the addition 
of soluble calcium salts. 
Hammarsten observed that milk curdles when it is heated to 130° 
j to 150° C. (see p. 344). Cazeneuve and Haddon (11) observed that 
I milk which had been coagulated at 130° C. became very acid. Ac- 
