34 



Mr. W. A. Jolly. Rejiex Times in the 



compare the results of mechanical stimulation with those recorded when the 

 stimulus is electrical and may be suspected of spreading, as Miss Buchanan (1) 

 points out, even so far as to affect nerve-fibres in connection with the motor 

 cells or nerve of the opposite side. 



A considerable number of observers have employed strychnine to raise the 

 excitability of the cord ; indeed, in the case of Wundt's (2) work the doubt 

 has been expressed as to whether he ever obtained the heteronymous reflex 

 in an undrugged preparation ; but the action of strychnine on the neural 

 mechanisms is so profound that responses and latencies observed under its 

 influence must be studied apart from those of the undrugged preparation. 



The range of temperature at which tliis investigation has been carried out 

 is higher than that generally employed with the frog, and the shortness of 

 the periods of delay obtained are to be explained to some extent on this 

 account. 



TJlc Spinal Frog. 



The spinal cord was cut aseptically and the wound allowed to heal 

 thoroughly. The reflexes were recorded at intervals while the frog survived. 

 The room temperature was noted, and observations at higher temperatures 

 were also made by keeping the frog during experiment in an incubator which 

 could be regulated to different temperatures. The frog's temperature was 

 then noted from a thermometer in the mouth. 



The reflex times are found to vary a good deal in the same frog and 

 between different frogs, and it is advisable to make a considerable number of 

 observations and to average the results. 



The factors which may be expected to influence the length of the reflex time 

 are the temperature, the length of the period of survival after operation, and the 

 length of the conducting nervous path, that is to say, the size of the animal. 

 Its age will doubtless also have an influence and can be estimated from the 

 size. Frogs were chosen of about the same size. They were allowed to live 

 as long as possible, and post mortem the nerves were dissected out and 

 measured. Towards the end of the period of survival the reflex times appear 

 to lengthen somewhat. 



The response in the spinal frog to a tap on the toes is a sudden sharp 

 flexion of the same leg and extension of the opposite leg. There is also 

 adduction of the limbs. The reflex is of a jerky character. 



The chief object of the investigation in the spinal preparation was to study 

 the time difference between the onset of homonymous and heteronymous 

 reflex activity of the hind limbs. In the spinal mammal it has been shown 

 that this interval is very brief, amounting only to about 0"001 second. In 

 the spinal frog I have found this difference to amount sometimes to as much 



