RESPIRATORY METABOLISM OF PLANARIA AGILIS. 211 



To test further whether the length of time during which the 

 animals lived in low oxygen concentration had any effect on the 

 percentage increase during the third period, the results of an 

 experiment in Table II. are given. The procedure was the same 

 as that in the experiment, Table I., except that a larger number 

 of bottles were used, with a greater range in the length of the 

 second period, the latter varying from 1.5 hours to 24 hours. 

 Roughly speaking, there is a slightly smaller average acceleration 

 of the rate in the lots of worms subjected to low oxygen for the 

 shorter periods than in the lots left in the low oxygen for the 

 long periods. The difference in the increase is in general quite 

 independent of the length of the period of low oxygen. 



COMPARISON OF THE RATES OF OXYGEN CONSUMPTION IN 

 AIR-SATURATED WATER BY STARVED AND FED ANIMALS 

 IMMEDIATELY AFTER HAVING BEEN SUBJECTED TO 

 Low CONCENTRATION OF OXYGEN. 



If we assume that the mechanism which determines the rate 

 of oxygen consumption can undergo an adjustment w r hen sub- 

 jected to low oxygen concentration, in such a way as to compen- 

 sate for the inhibitory effect of low oxygen on the rate of con- 

 sumption, then, would it not be possible to test this assumption 

 by comparing the acceleration, in rate of oxygen consumption, 

 after life in low oxygen, of two lots of animals one of which has 

 been previously subjected to repeated periods in low oxygen 

 concentration, while the other has been manipulated mechanic- 

 ally in exactly the same way without subjection to low oxygen 

 previous to the test? 



The data in the columns under lot A and lot B in Table III. 

 give the results of one test. Lot A was subjected to very low 

 oxygen during two alternate periods of eight hours each, while 

 lot B was manipulated similarly except that it was kept in aerated 

 water. The average actual increase in rate of oxygen consump- 

 tion by twenty animals during the third period is 1.08 c.c. oxygen 

 per gram per 24 hours in lot A, while in lot B it is 1.54 c.c. oxygen 

 per gram per 24 hours. The average increase is therefore 33 

 per cent, for lot A and 51 per cent, for lot B. A comparison of 



