96 PRACTICAL PHYSIOLOGY 



1000), and is gradually raised until the toes of one of the hind legs 

 dip into the acid ; this moment is noted, and then the interval between 

 the application of the acid and the withdrawal of the toes is measured 

 by a watch or a metronome (Fig. 92). After washing off the acid the 

 experiment is repeated with acid of the strength 1 in 500. In each 

 case the time of response is much longer than the true time of a 

 reflex action. 



CHAPTER XXIV. 

 THE ACTION OF STRYCHNINE AND OF CHLOROFORM. 



THE cerebrum of a frog is destroyed by means of Spencer Wells' 

 forceps, and then under the skin of the back are injected 10 minims 

 of a saturated solution of strychnine (1 in 6700). In two or three 

 minutes it will be noticed that the frog cannot readily recover its 

 hind legs after a jump, and soon the reflex excitability of the spinal 

 cord is so augmented that a slight touch or puff of wind upon the 

 skin causes a general spasm of the muscles. Convulsions quickly 

 follow, and the rigid body of the frog rests on the mouth and toes, 

 a position known as emprosthotonus. This attitude is due to the 

 different strength of the various muscles ; all are thrown into con- 

 traction, but the stronger overcome the weaker. The muscles are 

 somewhat relaxed after the spasms, but are again sent into tetanus 

 by the slightest touch applied to the skin. 



The tonic contractions are followed by prolonged twitches or clonus. 



If during the stage of convulsions a probe be pushed down the 

 vertebral canal, and thus the spinal cord be destroyed, the convulsions 

 cease at once, showing that the strychnine acts upon the ganglion 

 cells and their dendrites in the spinal cord. (See page 361.) 



The action of strychnine should be contrasted with that of chloro- 

 form. Under the skin of the back of a frog, whose cerebrum has 

 been destroyed by Spencer Wells' forceps, are injected 5 minims of 

 chloroform. The first effect is one of stimulation, but this stage of 

 excitement is quickly followed by marked inco-ordination and weak- 

 ness. In about ten minutes there is marked anaesthesia, paralysis, 

 and total absence of reflexes. If the frog be kept moist in a shallow 

 plate full of water, and covered by a bell jar, it may recover from 

 the effects of the chloroform in about eight or nine hours. 



