1915] Joseph Samuel Hephurn 147 



the interval 0° C. to 10° C, while it remained nearly constant, 

 with an average value of 1.9 1, for each interval of 10° between 

 10° C. and 50° C. 



Rennin. Selmi (24) noted that small quantities of rennin 

 coagulated milk, stored at 1° to 2° C, within 4 to 5 days. 



Camus and Gley (25) demonstrated that rennin exerts some 

 action on the casein of milk at 0° C. When rennin and milk 

 were mixed and held at that temp. for periods of ^ hr. or longer, 

 no precipitation of protein took place. Either lactic, acetic or 

 hydrochloric acid was then added in quantity insufficient to produce 

 a precipitate of protein, yet such a precipitate immediately formed, 

 showing that the rennin had given rise to the conversion of casein 

 into paracasein, the first stage of the enzymic curdling. 



Morgenroth (26) states that, even after the prolonged action 

 of very great quantities of rennet on milk at 0° C, the milk is not 

 curdled; however, it clots immediately if this mixture be brought 

 to a higher temp. The rennin, therefore, produces certain chem- 

 ical changes in milk during holding at 0° C, but the definite trans- 

 formation of the casein into its insoluble modification occurs only 

 at higher temp. 



Müller (15) prepared a sol. of rennin by extraction of the gas- 

 tric mucosae of pike with 0.25 percent hydrochloric acid sol. Five 

 drops of this extract were able to curdle 5 c.c. of unboiled milk in 2 

 min., at 40° C. ; in 53^ min., at 25° C. ; in 25 min., at 15° C, and 

 in 18 hr., at 7° C. At 0° C. no distinct curdling occurred, but a 

 finely flocculent condition of the milk was noted after incubation 

 for 5 days at that temp. This flocculation was apparent when the 

 tube was slowly moved to and fro. 



The time of curdling of milk is the sum of two factors, the time 

 required for the conversion of casein into paracasein and that re- 

 quired for the deposition of a visible coagulum; and the latter 

 phenomenon may require several days at lower temp., while occur- 

 ring in a few min., at most, at higher temp. Experiments were 

 carried out in such a manner that the first stage, or formation of 

 paracasein, occurred at 0° C, while the second stage, or Separation 

 of a visible coagulum, followed at a higher temp. (40° C). Both 

 the diluted rennin sol. and the milk were cooled at 0° C. Several 



