CONTEOL OF HEAD FORMATION IN PLANARIA 41 



whether or not the state of anesthesia is dependent on reduced 

 oxidations or accompanied by reduction in rate of oxygen con- 

 sumption, but to investigate the effects of the agents on the 

 stinmlation of section with reference to the degree of anesthesia 

 produced. For the sake of completeness, it may be stated that 

 in all the strong solutions employed there was distinct anesthesia 

 of the pieces. It has been sufficient for analysis of the factors 

 concerned in head determination to show that in the concentra- 

 tions employed these anesthetics, chloretone, chloroform, ether, 

 and chloral hydrate do prevent to an appreciable degree the 

 increase of oxidations attendant upon section. The exception 

 in the case of ethyl alcohol has already been dealt with. 



An extended discussion of the physical or chemical action 

 whereby this inhibition of stimulation is brought about would 

 lead us into the prevailing confusion of the numerous theories 

 of anesthetic action and avail nothing. For the question of the 

 nature of the physical or chemical action of the anesthetics in 

 the inhibition of stimulation is of no more importance in deter- 

 mining the effects of the anesthetics on head frequency than that 

 of the action whereby KNC reduces oxygen consumption in 

 Planaria, or the biological processes whereby young animals 

 maintain a higher rate of metabolism than old, or the manner of 

 action of the other agents and conditions that have been shown 

 to control head frequency. It is the quantitative effects on the 

 relative rates of metabolism in the X and Y regions that are of 

 primary importance. 



The data indicate that there is some sort of difference between 

 the nature of the stimulation of the X region and that of the Y 

 region, although the two are anatomically and physiologically 

 continuous. It is probable that at X the stimulation is general 

 for all tissues cut by the knife, body wall, gut, nerves, etc., but 

 not necessarily equal in each. The condition at X must be the 

 sum of the excitations of these tissues plus the effects of isolation 

 from all more anterior regions. The stimulation of tissues other 

 than nervous probably undergoes considerable decrement in its 

 transmission to regions more posterior, while the stimuli set up 

 bj'' section of the nerve tracts may be expected to be transmitted 



