172 STUDIES ON RESPIRATION. XX 



These salts were dissolved in water; the agar was then added and the 

 whole mixture sterilized in an autoclave. 



From agar the alga was transferred to a liquid medium prepared 

 in the same manner with the exception that 10 gm. of dextrose were 

 used in place of 10 gm. of agar. 



The cultures used in these experiments were grown for a period of 

 30 days in this liquid medium. The medium has a very slight alka- 

 line reaction and when tested showed no detectable buffer action. 



The algae were transferred to the respiration chamber^ along with 

 enough of the medium to make a volume of about 20 cc. The normal 

 rate of respiration was determined by taking the time necessary for 

 a change from pH 7.78 to pH 7.36. (This usually took about 2 

 minutes). When the normal rate of respiration was practically con- 

 stant the algae were separated from the medium by means of a centri- 

 fuge, which was run at a moderate speed. (Tests showed that this 

 centrifugation caused no injury.) The reagent was then added and 

 measurements of the rate of respiration were made at frequent inter- 

 vals until the desired point below the normal rate of respiration was 

 reached; the algae were then returned to the normal solution and at 

 intervals the rate of respiration was measured. 



The experiments were performed at 18 ± S^C. 



Fig. 1 shows the result of exposing the cells to hypertonic balanced 

 solutions. If the respiration does not fall below 60 per cent of the 

 normal, recovery is complete; if it falls lower recovery may be in- 

 complete, while if the rate drops too low there is no recovery. 



It was found in these experiments that there is no tendency for 

 recovery to complete itself even when the organism is kept for days 

 under the most favorable conditions. 



Fig. 2 shows recovery after exposure to solutions of chloroform. In 

 this, as in the previous case, no attempt was made to follow the res- 

 piration curve during the exposure since the interesting question was 

 the amount of injury produced and the subsequent behavior. 

 Curves A , B, and C show that if the injury is stopped when respira- 

 tion is from 58 to 70 per cent of normal, there is in every case complete 

 recovery within a period of about 4 hours and that the organism 



' This is the apparatus described by Osterhout. Osterhout, W. J. V., 

 /. Gen. Physiol., 1918-19, i, 17. 



