71 



as a rcsull of Ihc mass action, the \a ions later substitute 

 the K and Ca ions in llie cell body and tliey die. In othei* 

 words, NaCl is essential lor life, nevertheless Xadl is loxic 

 foi- the cells when it is present as the only salt. Phe 

 analog}', thai (lie growth |)romoting substances and growth 

 inliii)iting substances if such exist should act in some similai' 

 manner does not seem to be too hazardous a conclusion. 

 The work to he done in this line, is to find some indii'ccl 

 methods for investigating the nature of these sidistances, 

 methods which do not interfere too much with the physical 

 orientation of the colloidal or big-molecular solutions. The 

 methods w^hich are thought of here will probably tend in 

 the same direction as used in the investigation of the immune 

 bodies. The conditions are very complex and will require 

 much patience and ingenious observation for their eluci- 

 dation. 



GROWTH OF FIBROBLASTS AND HYDROGEN ION 

 CONCENTRATION OF THE MEDIUM. 



In connection with the investigation of the physico-che- 

 mical properties of the growth promoting substances, ex- 

 periments were undertaken to determine the role played 

 by the hydrogen ion concentration of the culture medium 

 in regard to the growth of fibroblasts cultivated in vitro 

 for a long period of time. 



The method used for the determination of the hydrogen 

 ion concentration in small amounts of fluid was that of 

 F e 1 1 o n 188). For the experiments fibroblasts from a 1—2 

 months old strain and fibroblasts from the old strain of 

 C a r r els 9 years old were used. 



The fibroblasts were cultivated for long periods of time 

 in medi'i of known hydrogen ion concentration. The vari- 

 ation in the hydrogen ion concentration of these media were 

 obtained in the following ways. 



Solutions of hydrochloric acid were prepared in such 

 concentrations that the addition of one drop to a certain 



