ACTION OF ALKALIES ON PLANARIA. 335 



The data given in Tables III. and IV. are graphed in Fig. 2, 

 the solid line representing the data of Table IV., the dashed line, 

 of Table III. The graph shows an acceleration of the rate of 

 oxygen consumption during the greater part of the exposure to 

 alkali, with an immediate drop at the end of each experiment on 

 return to normal water. 



SUSCEPTIBILITY EXPERIMENTS. 



The susceptibility method of determining differences in oxida- 

 tive rate in different parts of the same organism and between dif- 

 ferent individuals of the same species was devised by Child and has 

 been used extensively in this laboratory by him and his students. 

 The method is explained by Child ('24). Briefly, the organisms 

 to be compared are placed in toxic solutions of proper concentra- 

 tion or are exposed to lethal conditions and the various stages in 

 disintegration are recorded. In general, the higher the oxidative 

 rate, the shorter is the time before disintegration begins and the 

 more rapidly does the disintegration progress. The method is 

 therefore a rough means of comparing the relative rates of respira- 

 tory metabolism of comparable animals. Since the experiments 

 on oxygen consumption had shown that the respiratory rate of 

 Planaria is increased in alkaline solutions it seemed of interest to 

 determine whether or not worms so accelerated would be more 

 susceptible to chemical and physical agents than those respiring 

 normally in ordinary water. A few experiments were tried to test 

 out this point. Worms which had been kept for several hours 

 in water made alkaline to pH 9.0 with NaOH were compared as 

 to their susceptibility to toxic solutions and conditions while still 

 in alkaline solution with control worms kept and tested in ordinary 

 water or in solutions made up in ordinary water (pH about 8.0). 



Comparison of susceptibility differences between different lots 

 of worms is best accomplished by recording the progress of disin- 

 tegration in certain arbitrarily selected stages. In the following 

 experiments seven stages of disintegration were chosen: (i) worm 

 entirely intact; (2) disintegration at the margins of the head; 

 (3) from the end of marginal disintegration to complete disinte- 

 gration of the head ; (4) from the end of stage 3 to completion 



