73 



and a gi^'t'l acid. DillViTiil uiimhci's ol' di'ops of Ihc i-cspcc- 

 tivL' solutions acid, alkali or hut'fer) were added lo lid)es 

 holdinj^ Iht same ainoimls oT juice, and the hydrogen ion 

 concenlralion was tested. These dillerenl known reaclions 

 of Ihe juice gave a curve in which the amonnl of acid: 

 necessarv to obtain a certain hvdrogen ion concentration 



WP 



Fig. 4. 

 The different hydrogen ion concentrations of the media in which the fourth 

 passage of the old strain of fibroblasts is cultivated are indicated by the ab- 



scissae. The ordinates indicate the relative increase of growth, — . The dif- 



ferent hydrogen ion concentrations in the medium were obtained by adding 

 phosphate buffer solulions to the extract. 



between th( points found empirically could be calculated 

 by interpolation, (fig. 3). 



Equal volumes of the standardized buffer solulions and 

 of the tissue juice were used. To know what Ph resulted 

 in the tissue juice when il was mixed with its own volume 

 of buffer solution, the reaclions obtained gave a straight 

 line when a curve was plotted, and it was possible to cal- 



