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THE POPULAR SCIENCE MONTHLY. 



decisive in the matter : A frog is suspended by the head, and his legs 

 are allowed to dip into a vessel of dilute acid. After some time the 

 irritation causes the legs to be removed. The average time is ascer- 

 tained by frequent trials — then the animal's cord is cut just below 

 the medulla. The time which now intervenes between contact with 

 the acid and withdrawal of the limbs is much shortened, and the action 

 is decidedly more vigorous. Setschenow's experiments (1863) show 

 that this influence of the brain-centers can be greatly augmented by 

 direct irritation of the optic thalami. The rule respecting the reflex 

 activity of the cord would lead us to expect an increase of the activity 

 upon an increase of stimuli. This is true in general, but Wundt has 

 proved that the rule applies to those stimuli only that are carried to 

 the same part of the cord. If an afferent nerve in some other portion 

 of the body should be irritated simultaneously with the cord, reflex 

 action would entirely cease. 



We are now to consider certain activities of the cord which are the 

 most remarkable of all its manifestations. I allude to the experiment 

 first performed by Pfliiger. This experiment has been frequently re- 

 peated and variously interpreted. Pfliiger decapitated a frog, and 

 then placed some acetic acid on the animal's thigh. This headless 

 creature immediately wiped off the acid with the bottom of the foot 



,1. 



Fig. 8.— Upper StmFACE of the Cerebellfm. (Sappey. after Hirschfeld.) 1.1, superior " ver- 



snre ; 4, great fisscre of the upper surface wliich divides it into two principal segments; 5, 

 posterior of these segments in the form of a crescent; 6, 6, 6, 6, 6, anterior segment, quadri- 

 iateral, and composed of five secondary curved segments like the preceding — each of these 

 segments being composed of closely packed " laminse" of different sizes, separated by fissures 

 ofvarying depths; 7,7, sections of the cerebral peduncles; 8, ' posterior commissure" of 

 the cerebrum ; 9, corpora quadrigemina. 



of the same side. Pfliiger then removed this foot and again placed 

 acid on the same thigh. The animal at first, as though deceived, en- 

 deavored to rub away the acid in the same way as before. This being 

 impossible, the frog soon ceased trying that method, and seemed to be 

 seeking out some other plan. Finally, he made use of the foot which 



