BY DR. MICHAEL FOSTER. 413 



After a while these contractions pass off and the body and 

 limbs become once more relaxed. With each application of 

 the stimulus the same tetanus of the whole body is called forth, 

 no matter to what part of the body the stimulus be applied, or 

 what be the character of the stimulus. The purposeful nor- 

 mal reflex actions are lost in a complete spasm of the whole 

 body. 



It is possible to conceive that this result might be brought 

 out by an abnormal intensit}- of the impulses generated in 

 the afferent nerve by the stimulus, or by an abnormal irrita- 

 bility of the total muscular system, or by an abnormal condi- 

 tion of the spinal cord. That the last and not either of the 

 former two is the real cause, is shown by the following obser- 

 vation. 



Obs. XV. In a frog with divided medulla, ligature the hind 

 limbs, leaving the nerves free as directed in Chap. XXXI. for 

 urari, and afterwards inject a small dose of strychnia. 



In spite of the absence of the blood-current in the lower 

 limbs, the reflex actions will be as manifest in them, and as 

 easily brought about by stimulating them, as under ordinary 

 circumstances. But by the ligature the strychnia has been 

 prevented from having access to either the sensory nerves or 

 the motor nerves and muscles of the hind limb. Hence the 

 tetanic character of the reflex actions produced in them must 

 be due entirely to tlxe changed conditions of the spinal cord 

 itself. 



CHAPTER XXXIV. 



ON SOME FUNCTIONS OF CERTAIN PARTS OF THE 

 ENCEPHALON. 



MOST of the experiments illustrating this part of the sub- 

 ject, like those having to do with the conduction of impulses 

 through the spinal cord, are of a kind which the student can- 

 not be expected to perform for himself, and are consequently 

 not introduced here. Several observations, however, of a very 

 instructive character may be made on the frog. 



The brain of the frog may be considered, for present physio- 

 logical purposes, as consisting of three segments. We have 

 first the medulla oblongata (fig. 296 M. 0), and small cerebel- 

 lum c. next the optic lobes, L. Op., easily recognized in an 

 operation by the pigment contained in their pia mater, and 

 lastly, the cerebral hemispheres H. C lying over the corpora 



