238 



EXPERIMENTAL PHARMACOLOGY 



to size, relations, and the best way to dissect them out, 

 quickly. It is sometimes of much help to dissect out one 

 of these nerves and stimulate it to start up the respiration 

 in an animal that has stopped breathing but in which the 

 blood-pressure remains fairly high. 



EXPERIMENT XXXIX. 

 Hydrastine. (Frog: Spinal Cord.) 



1. With a pair of scissors cut off the front part of the 

 head of a frog (including the cerebrum) as shown in Fig. 

 220. Arrange the animal for recording muscular contrac- 

 tions as shown in Fig. 208. 



Cut on dotted line, just anterior to optic lobes 



Cerebrum 



rr.H. 



Fig. 220. Method for destroying (removing) the cerebrum but leaving the rest of the 

 brain intact in a frog. Note the position of the section. 



Under the skin of the back inject one cubic centimeter 

 of hydrastine (sulphate or hydrochloride) solution (one 

 cubic centimeter equals two milligrams). Wait two or 

 three minutes for absorption to occur and then start the 

 drum at a fairly rapid speed. After a little while there 

 should be a marked reaction. Try to record the firtt action 

 manifested by the frog. Finish the first round on the drum, 

 then lower the drum and take a second round. How do the 

 reactions shown on the last round compare with those in 



