174 



STUDIES ON RESPIRATION. XX 



a lowered rate of metabolism because of the treatment. In order 

 to throw light upon this point it was decided to resort to staining 

 methods. Methylene blue was found to be convenient since it would 

 quickly stain the algae that had been killed by the chloroform or the 

 hypertonic salt solutions, but did not stain the living cells during a 

 short exposure to the dye. In the normal culture some of the cells 

 (from 5 to 8 per cent) were stained. 



Fig. 2. Curves showing the rate of respiration of Chlorella after treatment 

 with chloroform. Curves A, B, and C were obtained by using 0.225 per cent 

 chloroform (by volume); Curves G and F with 0.27 per cent; Curve B, with 0.36 

 per cent. The first point on each curve denotes the per cent to which the res- 

 piration had fallen when the algae were transferred from the solution of chloroform 

 to the normal medium. The ordinates denote the rate of production of CO2 

 expressed as per cent of the normal; the abscissae, time in hours. Each curve 

 represents a typical experiment. 



Cultures of the same age were selected and the normal respiration 

 was measured in the usual manner. Each culture was then treated 

 with chloroform of sufficient strength to decrease the respiration of 

 the algae. The algae were then subjected to the stain (for 3 minutes) 

 and it was found that not more than 8 per cent of the cells were ever 

 stained,^ no matter whether the respiration had fallen to 70 per cent 

 or to 10 per cent of the normal rate. The time of exposure of the 



* The cells were counted by means of a hemocytometer. 



