RESPONSIVE LIFE OF ORGANISMS 467 



follows: some, with the cerebral hemispheres carefully 

 removed (other parts of the nervous system being left un- 

 injured) ; others, with the cerebellum also removed; others, 

 with the spinal cord severed at its junction with the 

 medulla, the purely reflex apparatus thus being isolated. 

 Specimens will require to be properly handled and cared for 

 until used. The specimens may be used by different stu- 

 dents in succession, or if preferred, the demonstration may 

 be made by the instructor. 



While the preceding account of the nervous system has 

 followed logically the building up of it, these experiments 

 will of necessity follow the reverse order. The student 

 should first of all be familiar with the living normal frog, so 

 as to be able to judge of changes produced in its actions by 

 the loss of brain parts. 



1. Observe a frog that has lost its hemispheres only, 

 noting especially its want of volitional activity. Test its 

 power for correlated movement by throwing it into water 

 and making it swim; by tilting the support on which it 

 sits, making it balance itself; by making it jump. Try to 

 determine experimentally whether it can see and hear. 

 See what it will do with a bit of suitable food (such as a fly) 

 placed in its mouth. 



2. Try the same experiments with a frog that has lost 

 also its cerebellum, noting especially the effect of this loss 

 upon the coordination of its movements. 



3. Observe how the severance of the brain from the cord 

 has affected the tone of the body as a whole. Hang a 

 brainless frog up by its head for convenience in manipula- 

 tion and test its body at various points for reflex responses 

 to stimulation of the skin. A small brush dipped in dilute 

 acid may be used to touch the skin, and the acid may be 

 immediately removed with a wet sponge. 



