62 PHYSICAL CHEMISTRY IN MEDICINE. 



the colloid and determines the condition. in which the 

 colloid will ultimately be found. In other words, a colloid 

 seems to remember more or less perfectly a change that 

 it has suffered, just as does living matter. If gelation 

 and melting followed the same course, only in opposite 

 directions, then a gelatine, when it has returned to its 

 original temperature, should also be existing in its original 

 state, no matter in which direction it had previously 

 suffered a change in temperature. That we have to do 

 in this case with reversible changes that follow different 

 paths is evidenced by another property of this change 

 in state. If one compares the curves indicating the 

 melting- and gelation-points of gelatines of different 

 concentrations, obtained by plotting the concentrations 

 upon the abscissas and the corresponding melting- and 

 gelation-points upon the ordinates, it is seen that the 

 two processes are dependent in different ways upon the 

 concentration of the gelatine. The gelation curves follow 

 an approximately straight line; the melting curves, on 

 the other hand, rise gradually, but in a decreasing degree, 

 above the abscissa. 



In contrast to the previously described simple or homo- 

 drome antagonistic reactions, which follow the same 

 course in either direction and which behave at any stage 

 as mathematical values having different signs, we are 

 dealing in this case with complex or heterodrome antag- 

 onistic reactions, which reach their respective end states 

 along different paths. (See Figs, i and 2.) 



In what follows we will make use of these simple dia- 

 grams in characterizing the antagonistic reactions. 



Heterodrome reactions of a chemical nature play 

 an important role in the changes that go on in living 



