DEPARTMENT OF EMBRYOLOGY. 79 



sulphate and sodium arsenite, acquires in the course of two days a definite 

 tolerance for strong doses of these two poisons. In dealing with the entire 

 organism it is generally impossible to determine whether a given tolerance is 

 intracellular or extracellular. In tissue-culture, however, this can be tested 

 directly and in these experiments the tolerance was found to be intracellular. 

 It is shown that ordinary embryonic mesenchyme cells have a certain amount 

 of natural tolerance for the two inorganic poisons used and that an increased 

 or acquired tolerance can be produced by growing the tissue in dilute solutions 

 of the substances. The effect of the poisons was determined on the one hand 

 by the extent and frequency of growths in the cultures and the maximal 

 duration of life as compared with control cultures; on the other hand, by the 

 time required to kill cells cultivated in these weak solutions by treating them 

 with strong solutions, as compared with the time required to kill the cells in 

 control cultures treated with the same solution. 



Hydrogen-ion Concentration of Tissue-Cultures. 

 Bacteriologists have found that in growing bacteria there is an optimum 

 hydrogen-ion concentration for their media and a limiting or final concentra- 

 tion at which growth activity ceases. In order to compare the metabolism 

 of tissue-cultures with that of bacteria, and also to determine the effect of 

 bacteria on tissue-culture growths, Mrs. Lewis and Dr. L. D. Felton have 

 experimented with media of different concentrations and observed their rela- 

 tion to the activity of the growths. In order to test tissue-cultures for H-ion 

 concentration, it was first necessary to devise a method by which the deter- 

 mination can be accurately made where there is only a small amount of fluid 

 available for the test. A satisfactory procedure was worked out by Dr. 

 Felton; this consists of a colorimetric method in which a piece of white opal 

 glass is used as a background on which single drops of fluid are tested with a 

 series of standard buffer solutions. It was found that cultures of embryonic 

 chick tissue, when explanted into a solution having a hydrogen-ion concentra- 

 tion of 4 to 5.5, seldom showed any growth, while those in solutions having 

 a concentration of from pH 6 to pH 9 usually showed abundant growth. The 

 optimum hydrogen-ion concentration seemed to be about pH 7. Regardless 

 of the initial hydrogen-ion concentration of the medium, where the solutions 

 contained not more than 0.5 per cent dextrose, the cultures showing healthy 

 and extensive growth tended to be neutral, those that had failed to grow 

 usually became slightly acid, and those that had exhibited extensive growth 

 and then degenerated were most frequently slightly alkaline. The final 

 hydrogen-ion concentration varied, however, according to the amount of 

 dextrose in the solutions. When 1 per cent or more dextrose was added to 

 the medium, the cultures were often found to be acid when death took place. 

 The addition of some dextrose to the medium proved to be necessary for a 

 healthy growth of cells over a period of time longer than three days. There 

 was some growth even with 5 per cent dextrose, but the cultures in solutions 

 containing between 0.5 and 1 per cent exhibited the greatest proliferation of 

 cells and remained healthy for the longest periods of time. 



Adhesive Quality of Cells. 

 In studying the factors concerned in the migration of cells from the explant 

 in tissue-cultures, Dr. W. H. Lewis calls attention to the important role 



