736 DR FRASER ON THE PHYSIOLOGICAL ACTION 



In the further investigation of the effect on reflex movements, there is no 

 process which yields so conclusive results as that in which frequent measure- 

 ments are made of the interval that elapses between the application of a stimulant 

 to the extremity of an afferent nerve and the resulting reflex contraction* 



Experiment XXXVIII. 



The spinal cord was divided at the occiput of a frog, weighing 460 grains. It was sus- 

 pended by the lower jaw, and the reflex activity tested by dipping the web of both posterior 

 extremities into dilute sulphuric acid (ten minims oil of vitriol to twelve oz. of water). The 

 exact time which elapsed between the contact of the foot and the resulting reflex movement was 

 ascertained by the beats of a metronome, set at 100 in the minute. Before the administration 

 of the poison, the reflex movement occurred in twelve beats. Two grains of extract, in water, 

 were injected into the abdomen. 



In 5 minutes, reflex movement occurred in 15 beats. 



10 „ „ 31 „ 



15 „ „ 40 „ 



20 „ „ 57 „ 



25 „ „ by „ 



30 „ „ 82 „ 



35 „ „ 106 „ 



40 „ „ 134 „ 



45 „ „ 165 „ 



50 „ „ 181 „ 



55 „ „ 1J2 „ 



1 hour 5 min. no reflex movement after 250 „ 



1 ,, 15 „ strong acid caused no movement. 



The sciatic nerves were then exposed ; and weak and carefully localised galvanism applied 

 to either trunk caused energetic contractions of the limb below the portion stimulated, which 

 could be obtained until two hours after the injection of the poison. 



It seemed important to ascertain the coincident changes that take place in 

 the heart's action ; and for this purpose several experiments were undertaken, of 

 which the following is an example. By a slight adjustment of the frog's body, 

 the cardiac impulses are easily seen and counted. 



Experiment XXXIX. 



A frog, weighing 460 grains, was suspended by its lower jaw. The average of the cardiac 

 contractions, during ten minutes, was forty-five per minute. The two feet were alternately 

 stimulated, every five minutes, by contact with dilute sulphuric acid (10 minims of oil of vitriol 

 to 12 oz. water) ; a vessel containing the acid being gently raised so that the fluid covered the 

 whole foot. A metronome, set at 100 in the minute, was employed to determine the interval 

 between the application of the irritant and the resulting reflex movement. 



* This method of examining reflex activity seems to have been first recommended by Von 

 Turck in 1850 (Ueber den Zustand der Sensibilitat nach theilweiser Trennung des Riickenmarks) ; 

 and its value has been brought more prominently into notice by Dr J. Setschenow (Physiologische 

 Studien iiber die Hemmungs-mechanismen fiir die Reflexthatigkeit des Riickenmarks im Gehirne 

 des Frosches, Berlin, 1863). 



