South African Claiued Frog. 



41 



small oscillations occurring at a rate of about 216 pei' second. This record 

 was made at a temperature of 18*^ C. Some curves show a double summit, 

 as though one twitch were followed closely by another. These resemble 

 some of the curves figured by Miss Buchanan (1). Sometimes the records 

 are complicated in such a way as to suggest that the reflex is composed of a 

 series of twitches. Occasionally, there is visible in the records of the 

 homonymous effect a small initial deflection, following the stimulus after an 

 interval of a few ex. It was at iii'st thought that this might be some 

 fortuitous effect upon the string due to the mechanism of stimulation, which 

 involves the release of an electromagnet, but precautions do not prevent its 

 occasional appearance, and it must be attributed to some form of direct 

 stimulation of the foot by the hammer tap. Its very short latency is 

 consistent with this. 



The twitcli-like nature of the response is wliat one would expect from the 

 jerky movement of the muscles in the spinal preparation. The succeeding 

 series of small rapid oscillations indicates that there is also an element of 

 tonic contraction involved. 



TJte DecercbniU Frog. 



The cerebral hemispheres were removed aseptieally and the wounds 

 allowed to heal. The frogs were preserved until they died, usually several 

 months, and the reflex times were tested at intervals. The wicks of the 

 non-polavisable electrodes were applied over the skin, either at thigh and 

 ankle or knee and ankle. The reflex movement elicited by stimulating the 

 toes in the decerebrate animal has not the twitch-like character which it 

 assumes m the spinal frog. The reflexes are not obtained with the same 

 certainty as in the spinal frog. The heteronymous reflex sometimes fails 

 even when the stimulus used is the nocuous form of a strong squeeze. In 

 other cases the reflex is delayed very considerably. Under these circum- 

 stances, it seemed desirable to make a number of alternated observations of 

 crossed and same-side reflex activity at intervals of a day or two, and to 

 average the results, in order to obtain a measure of the time difference 

 between the commencement of the two reflexes, rather than to rely upon the 

 differences found in individual pairs of responses. 



With regard to the delayed heteronymous responses, such times as the 

 following have been recorded : 43'1 a at 22° thirty-eight days after decerebra- 

 tion ; 45*4 a at 26°, twenty-nine days after decerebration ; and 55"2 a at 

 19'6°, ninety days after decerebration. Such long delays have not been 

 found in spinal preparations, but in the intact frog I have found periods of 

 52 cr, 57'5 0-, and 59 cr, and also some of a still greater duration, viz., 82'5 a-, 



