of small amounts of rennin into the blood of animals, Morgenroth 
(36) obtained an antirennin. According to Fuld and Spiro (37) the 
antirennin of normal horse serum prevents the coagulation of milk by 
binding the calcium ions. Arrhenius is therefore of the opinion that 
in these reactions rennin coresponds to the toxophorous group, the 
calcium ions to the haptophorous group of a toxin, and the antirennin 
to an antitoxin. 
Many additional facts concerning the rennin ferment are known. 
Like other ferments, it is affected b}^ heat, and the rate of the rennin 
coagulation is determined both by the quantity of rennin acting and 
by the temperature. It has been shown that the ferment can with- 
stand a temperature of — 180° C. without injury. At temperatures 
higher than 44° C. the ferment gradually loses its activity, and expo- 
sure to a temperature of 50° to 60° C. for a considerable tune has been 
found to be more harmful than a short exposure to a higher tempera- 
ture. The effect of temperature is also determined by conditions sur- 
rounding the ferment, whether it is moist or dry, and also by the 
reaction of the solution containing the ferment. In the dry state it 
can withstand a temperature of 100° to 140° C. Its destruction by 
heat has been found to follow the law for a monomolecular reaction. 
The influence of temperature on the rennin coagulation has been 
studied by Fuld (29). Some of his results are given in the following 
table : 
Temperature ° (C.). 
Time (see ). 1 ] 
k, observed. 
k, calculated. 
25.05 
54 
32 
385 
185 
80 
312 
327 
35 
17 
588 
574 
40 
10.2 
980 
980 
44 
9 
i,m 
680 
1,491 
2,742 
50 
14.7 
(The values of k, observed equal 10,000 divided by time.) 
It will be observed that there is *a good agreement between the 
observed and the calculated values up to 40° C. Above this tem- 
perature the observed values of k become smaller than the calculated 
values on account of the gradual destruction of rennin by heat. 
In 1870 Segelke and Storch (38) showed that rennin coagulates 
milk in intervals which are inversely proportional to the concentra- 
tion of the rennin solution. This conclusion has been confirmed by 
the later work of a number of observers. Thus Lorcher (39) obtained 
the following results from his measurements; 
