On the Nervous System of Cassiopea Xamachana. 



159 



were also interfered with to such an extent that respiration practically 

 ceased. Active half-disks were capable of maintaining at least inter- 

 mittent pulsation until the hydrogen-ion concentration had become 

 0.159 X10~ 7 (P H = 7.8). Nearly all the determinations of the H con- 

 centration were made by means of color comparison with tubes of 

 known H concentration prepared by Hynson Westcott & Dunning, 

 from buffer mixtures standardized by J. F. McClendon, containing 

 mixtures of phosphates and borates using thymolsulfonephthalein for 

 concentrations above P H = 8 and phenolsulfonephthalein for concen- 

 trations below P H = 8. These tubes were in no part of their range 

 graduated more closely than P H = 0.1, so that no very fine readings 

 could be obtained except by estimating fractions of this unit, which 

 could not be done with any considerable degree of accuracy. 



INFLUENCE OF SENSE-ORGANS ON THE CHANGE IN RATE OF 

 PULSATION IN RESPONSE TO CHANGES IN TEMPERATURE. 



The studies of Harvey (1911) and Mayer (1913) have shown that 

 when Cassiopea is slowly heated the rate of nerve-conduction increases 

 from about 18 C. to about 36 C., after which there is a rapid decline 

 hi the rate. Recovery of the 

 medusa is impossible if the 

 temperature is carried much 

 above 40 C.; indeed, when 

 cooling is begun before a fatal 

 temperature is reached the 

 normal rate of pulsation does 

 not return even when the me- 

 dusa has been kept at normal 

 temperature for several days. 

 In its general features the 

 curve for the rate of nerve- 

 conduction in Cassiopea re- 

 sembles that for enzyme ac- 

 tion, as was pointed out by 

 Harvey, and as shown for the 

 pulsation-rate of the verte- 

 brate heart (Knowlton and 

 Starling (1912) etal). 



Since Mayer (1908) has 



shown that the initiation of 



the stimulus for pulsation 



takes place in the sense-organs 



through a definite chemical 



reaction, it was thought possible that if a sense-organ were subjected 



to changes in temperature while the body of the disk was kept at a 



FIG. 14. Curves showing averages of all determina- 

 tions of effect of change in temperature on active 

 and activated halves of the same disk. 



