l62 C. M. CHILD. 



larger extent than either chloretone or ether in my experiments 

 up to the present time because it has given characteristic results 

 and because it has seemed desirable to obtain fairly complete data 

 concerning the effect of a mild anaesthetic upon various regions 

 of the body, on pieces of different size and age and in different 

 physiological condition as a basis for comparative work with sub- 

 stances with stronger anaesthetic properties. It is my intention to 

 extend the work to various other groups of substances which 

 have a definite effect on metabolism. In most of the work of this 

 kind the effect of only a short period of time in the given medium 

 has been determined. It seems to me particularly desirable to 

 determine more exactly the effects of continued existence in media 

 of various constitution on development and regulation. By such 

 means it should be possible to advance a step further in our analy- 

 sis of the processes of differentiation, localization and growth. 



I. Methods. 



The method of use of the anaesthetics, all three of which are 

 more or less volatile, is as follows : Not more than ten pieces of 

 the planarian are placed in a Stender dish holding about 250 c.c. 

 and with ground edge and cover with ground groove exactly 

 fitting the edge. This dish is filled to three fourths of its depth 

 with the mixture of the desired concentration, some of the fluid 

 is poured over the under side of the cover so as to wet its surface 

 and fill the groove, and the cover is placed in position at once. 

 Several of these dishes are placed in larger glass jars with 

 ground edges, a liter or more of the fluid is poured over them 

 into the jar and it is at once sealed by means of a glass plate on 

 which a ring of vaseline corresponding to the edge of the jar 

 has been smeared. In this way decrease in concentration is 

 avoided as far as possible. Furthermore the fluid is renewed at 

 least every forty-eight hours and the mixture of the desired 

 concentration is always made up immediately before using. It 

 has been found desirable to keep the temperature as nearly as 

 possible constant, except where its influence on the results was 

 to be determined. In most of my experiments the temperature 

 has ranged between 17° and 20° C. but rarely beyond these 

 limits. Rise in temperature much beyond 20° C. increases the 



