LOCALISATION OF GEO-PERCEPTIVE LAYER 491 



the advance of the season. This may partly be due to 

 unfavourable season, and partly to hi^'h temperature. In 

 the middle of the season the responses were extremely 

 feeble on warm ilays, but on cool mornings they became 

 suddenly enhanced, to decline once more by the middle 

 of the day. I coukl sometimes succeed in enhancing 

 (he sensitiveness by placing the specimen in a cold 

 chamber. It thus appeared that certain internal change 

 unfavourable for geo-perception takes place at high tem- 

 peratures, and that the sensitive condition could some- 

 times be restored by artificial cooling. Hut later in the 

 season, ihe internal change, whatever it may be, had pro- 

 ceeded too far, and artificial cooling did not restore the 

 sensitiveness of the specimen. What are the physico- 

 chemical concomitants which distinguish insensitive speci- 

 mens, in which the electric indications had declined almost 

 to the vanishing point ? 



TEST OF INSENSITIVE SPECIMENS. 



I shall now d 'scribe the various physico-chemical con- 

 comitants which accompany the condition of relative 

 insensibility. I have found three different tests ; the electric, 

 the geotropic, and the microscopic, by which the sensitive 

 could be distinguished from the insensitive condition. The 

 following tests were made on insensitive specimens. 



Electric test : Experiment 187. — By the end of August 

 the geo-electric indications given by the probe had, as 

 stated before, almost disappeared. The tonic condition 

 of the specimen, heloiv par, was independently revealed by 

 the response to prick of the probe ; this, in vigorous 

 specimens, is by an electric response of galvanometric 

 negativity. But the response to prick in sub-tonic 

 specimens is very different. I find that when the physio- 

 logical condition of the tissue falls below pai\ the sign of 

 response undergoes a reversal into one of galvanometric 



