Not satisfied with the mère knowledge of the optimum- 

 curve one has asked the cause of the inversionpoint in 

 the eurve and whether or no the occurrence and position 

 of this inversion point are susceptible of further explanation. 



In conséquence the optimum-curve itself has been ana- 

 lysed. With regard to the actions of enzymes Duclaux 

 in 1899 gave his opinion on theoretical grounds that the 

 optimum-curve owes its origin to the summation of two 

 curves. One of thèse curves would represent the continu- 

 ally increasing reaction-velocity, the other would show the 

 even more rapid increase of the harmful influence of 

 higher températures. In 1905 Black m an further develo- 

 ped this theory, added new ideas and adduced facts and 

 figures in support of his argument. 



As Blackman's Une of thought has been taken as a 

 guide for this investigation, it is necessary to give his 

 considérations somewhat in détail. In the first place 

 Blackman criticizes the conception of the optimum as a 

 primary relation which holds good universally between 

 température and a physiological process, and arrives at 

 the conclusion that the optimum does not express a pri- 

 mary relation and must vary with the time of observation. 



His starting-point is the rule that the reaction-velo- 

 city of certain chemical transformations increases two- 

 to three-fold for every 10° C. rise of température. This 

 law, known as van 't Hoff's law, holds good m vitro 

 for ail those ]-eactions which take place slowly in aqueous 

 solutions and resemble the reactions in- the organism. 



As early as 1901 Cohen pointed out in his „Vortrage 

 fur Aerzte ûber Physikalische Chemie," that this law may 

 also be applied in biology; and he quoted some investi- 

 gations from botany and zoology proving its validity. 



Between 1905 and 1910 Kanitz published several papers 

 on this subject and found that van 't Hoff's law was 



