214 Profpssor Svantc Arrhenius [June 0, 



solution of HCl, 1 c.c. of a solution containing different quantities 

 (q) of pepsin. The mixture was heated for 2 hours to 86" 6° C, and 

 then put in an ice-safe, where it soon solidified, if it was not digested. 

 By trying a great number of mixtures containing different quantities 

 (q) he found the least quantity (q^) necessary to cause just that 

 degree of viscosity, as described above, in two hours. In the same 

 way he determined the quantity (qi) necessary to give the same 

 degree of fluidity in four hours, and so forth. He found the following 

 values : — 



Time, t .... 2 4 8 14 20 24 



Quantity of pepsin, rj . 0-47 0-26 0-13 0-07 0-045 0-038 

 Product, g.i . . . 0-94 1-04 1-04 0-98 0-90 0-91 



The product (q.t) is not wholly constant, but very nearly so. The 

 law for common monomolecular reactions, where the rate of chemical 

 change is proportional to the quantity of the acting substance, is 

 fulfilled. In a later experiment Madsen maintained the quantity (q) 

 constant, and determined the time necessary for the given degree of 

 digestion at a given temperature. This time is evidently inversely 

 proportional to the velocity of reaction. He found the same regu- 

 larity in this case as for the change of other chemical reactions 

 with temperature (cf. above). 



Similar regularities were found for the digestion of gelatin by 

 means of trypsine or an antigene, produced by pyocyaneus-bacilli, in 

 the coagulation of milk by means of rennet, in the coagulation of 

 blood-plasma, etc. It is sometimes found that the velocity of reaction 

 has a maximum at a certain temperature, which is explained by the fact 

 that the spontaneous decomposition of the antigene increases very 

 rapidly with lising temperature and much more rapidly than the re- 

 action investigated. At high temperatures, tlierefore, the time during 

 which the antigene, e.g. rennet, really has opportunity to react, is 

 practically zero, and the observed reaction extremely small. From 

 this circumstance the occurrence of a maximum is easily understood. 

 In the coagulation of milk by means of rennet, Fuld observed such 

 a maximum at 43° C. In reactions of living cells on other substances 

 such maxima are generally found at about 40" C, at which tempera- 

 ture the cells slowly lose their vital activity by the coagulation of 

 their protoplasmatic content. Such maxima are often found in this 

 department of science ; they depend on the concurrence of two 

 simultaneous processes which act in opposite directions. In many 

 of these processes, for instance the coagulation of milk or of blood- 

 plasma, the presence of certain salts, in most cases salts of calcium 

 (salts of barium or strontium act in a similar manner), play an 

 important role. Reichel and Spiro found for the coagulation of 

 milk that the necessary time is inversely proportional to the concen- 

 tration of calcium-ions in the solution. 



