1913.] AND FUNCTION IN THE NERVOUS SYSTEM. 491 



glucose I per cent., bouillon lo per cent.). After a little practice the 

 operation of removing the embryo from the egg and placing it in the 

 dish, without either delay or unnecessary shock, may be easily per- 

 formed. It is obvious that stimuli of a purely mechanical nature up 

 to a certain degree of intensity seem to be less injurious than those 

 caused by variations in temperature. 



The efifect of rapid changes in position upon the action of the 

 heart during the period represented by embryos of from 12-16 

 somites is almost a negligible quantity. Embryos that were whisked 

 rapidly about in a dish by means of a camel's hair brush showed no 

 disturbance of cardiac activity ; provided of course that the tempera- 

 ture of the solution in which they were placed remained constant. 



The primitive responses of these organisms show certain inter- 

 esting features when elicited in response to various chemical sub- 

 stances used as irritants. In this connection the action of a number 

 of different substances was observed, while that of two was studied 

 in detail. The substances selected for more detailed investigation 

 were strychnia sulphate, an important inorganic nerve stimulant, and 

 thyroid extract, representing organic substances toxic for nervous 

 tissues. After it became possible to eliminate the error attributable 

 to such slight differences in temperature as are apt to occur during 

 manipulation it was found that these two dissimilar substances were 

 strikingly alike in their physiological action upon the heart, if used 

 at a time prior to the development of the nervous system. Even 

 when employed in minute quantities the characteristic accelerating 

 action upon the heart was not observed. As will be noticed in 

 studying the records in the case in which the smallest doses were 

 administered the rate of the cardiac pulsations was not disturbed for 

 some time and only after the elapse of from one to two hours did the 

 action of the heart begin to show symptoms of sagging. In all cases 

 an accelerating action seemed to be entirely absent. 



Probably the most intimate correlation which we have yet been 

 able to establish is in connection with the development of the 

 peripheral nervous system. In the case of such substances as cocaine 

 and eucaine we have already shown (op. cit.) that there is no inhibi- 

 tory and reversible action in selachian embryos following ordinary 



