CHAPTER XXVII 

 Reflex Action : Reaction Time 



A FROG, the brain of which has been removed, 1 is used for the follow- 

 ing experiments. Note the position of the animal when placed on 

 the table, and the absence of spontaneous movements. Suspend the 

 preparation by the lower jaw (Fig. 85). Have ready a large jar or 

 beaker of water (a), a small beaker of 2 per 1,000 sulphuric acid (6), 



Nares. 



Olfactory lobes. 

 Cerebral hemispheres. 



.Thalamus with pineal gland. 



Optic lobes. 



- Cerebellum. 



; - Medulla oblongata. 



Spinal cord. 

 FIG. 84. Brain of frog in situ, exposed by removing the roof of the cranium. 



and some small pieces about 2 mm. square of filter paper, 

 moistened with 5 per cent, acetic acid. A watch, with seconds hand, 

 or a metronome is also required. 



Effect of strength of stimulus. Gently pinch the toe of one foot 

 with forceps ; the leg is drawn up. When again quiescent, pinch 

 the toe more firmly ; not only the one pinched, but both legs are 

 drawn up, and there may also, be a movement of the upper limbs 

 (spread of excitation in cord). 



1 For some of the experiments on reflex action the whole contents of the 

 skull are destroyed. This can be done without haemorrhage by inserting a 

 sharp-pointed plug of wood through the occipital foramen. For other experi- 

 ments only the cerebrum or brain proper is destroyed, the optic lobes and 

 medulla oblongata being left. This is effected either by crushing the anterior 

 part of the skull with Spencer Wells forceps ; or by opening the skull and 

 removing the hemispheres in an anaesthetised animal ; or by cutting away all the 

 part of the skull in front of the tympanic membranes with a razor. 



