36 PHYSICAL CHEMISTRY IN MEDICINE. 



difficulties; nor does it furnish even the possibilities of a 

 complete understanding of many important phenomena. 

 In spite of this, however, numerous fundamental investi- 

 gations, such as those of HAMBURGER and KOPPE, con- 

 tinue to retain great value, representing as they do the 

 first experiments undertaken in the study of a new subject. 

 The principles employed in these investigations approxi- 

 mate actual conditions only more or less coarsely; they 

 fail, however, to explain details because conditions for their 

 employment in the organism are satisfied only in part. 

 This fact leads, however, to the recognition of new 

 physico-chemical peculiarities of living matter, as illus- 

 trated, for example, in such discoveries as the biological 

 significance of the distribution law. 



The osmotic relations between animal cells and their 

 surrounding media were studied for the most part on 

 red blood-corpuscles. These give off their red coloring- 

 matter in dilute salt solutions as soon as the concentration 

 of the salt drops below a certain value. The lowest con- 

 centration of different salt solutions which just prevent 

 the "laking" of blood are said by HAMBURGER to be 

 isotonic with each other and are regarded as bringing 

 about the same degree of swelling in red blood-corpuscles. 

 .Since a determination of the osmotic pressures of such 

 isotonic salt solutions by physical methods (determina- 

 tion of the freezing-point) showed them to be about the 

 same, the " blood-corpuscle method" was looked upon 

 as a universally applicable procedure for determining 

 osmotic pressures. An extension of this method to a 

 large number of crystalloids soon showed, however, that 

 physical and physiological isotonicity are identical in 

 only a few substances, the majority showing differences 



