42 J. WILLIAM BUCHANAN 



with less decrement. (For a discussion of decrement in trans- 

 mission of stimuli, see Verworn, '13, chap. VI; also Child, '20 c, 

 chap. IV.) One cannot say whether or not all the tissues other 

 than nervous transmit stimuli equally. In any event, the stimu- 

 lation of the Y region must be the result of some sort of trans- 

 mission of stimuli arising in the X region, but that the stimuli 

 are not transmitted solely by nerves, or else nervous stimuli in 

 these animals undergo marked decrement is suggested by the 

 fact that short pieces are more stimulated than long pieces from 

 the same region. 



There is evidence of a difference in the nature of the changes 

 in the X and Y regions to be found in Child's results on head 

 frequency w^ith KNC and my own results with chloretone, chloro- 

 form, and ether. With both KNC and chloretone the decreases 

 in head frequency in the A pieces are marked and may easily be 

 extended to B or even C pieces by extending the period of ex- 

 posure or increasing the concentration. KNC is a general 

 protoplasmic poison and inhibitor, but not a particularly good 

 anesthetic, while chloretone might be called a general protoplas- 

 mic anesthetic, i.e., its effectiveness is in a large measure inde- 

 pendent of the degree of specialization of the nervous system. 

 Chloroform and ether, on the other hand, are powerful anesthe- 

 tics in the strict sense, i.e., they act more intensively on the highly 

 specialized nervous system than on protoplasm in general. 



In the pieces of Planaria the changes in the X region following 

 section are general protoplasmic changes w^hich lead to dediffer- 

 entiation, cell division, and growth; while the changes in the Y 

 region represent a temporary excitation which is certainly in a 

 large measure nervous in character. We may expect, then, that 

 agents which are general protoplasmic inhibitors will affect the 

 X region more than those which are chiefly nervous inhibitors. 

 The first group, the general protoplasmic inhibitors, should be 

 more effective in producing decreases in head frequency in A 

 pieces and less effective, except perhaps in low concentrations 

 (KNC), in producing increases in the C pieces. The nervous 

 inhibitors, on the other hand, should be less effective in producing 

 decreases in head frequency in the A pieces and more effective 



