174 



PRACTICAL PHYSIOLOGY 



FIG. 164. Brodie's bellows recorder. 

 The bellows are made of aluminium plates and peritoneal membrane. 



CHAPTER XXXVI 



THE FUNCTIONS OF THE ANTERIOR AND POSTERIOR 

 ROOTS OF THE SPINAL CORD. THE MAJENDIE LAW 



The researches of Majendie showed that the anterior roots of the 

 spinal cord were motor, and the posterior were sensory ; the former 

 nerves are efferent, carrying nervous impulses from the spinal cord 

 to the periphery, the latter are afferent, carrying impulses from the 

 periphery to the spinal cord. This law can be proved by experiments 

 upon a brainless frog, but careful dissection and manipulation are 

 necessary. 



The following are the several stages in the experiment. A small 

 pair of electrodes is made by passing the bared ends of two pieces of 

 fine insulated wire through a piece of cork, and the induction-coil is 

 arranged for single shocks. The cerebrum of a large frog is destroyed 

 by compression with a pair of Spencer Wells' forceps, and then the 

 frog is placed belly-downwards upon a cork board, and is confined to 

 this position by a piece of wet flannel fastened down tightly by pins. 

 A slit is made through the flannel in the line of the vertebral column, 

 and the skin is reflected as far as the end of the urostyle. The ilium 

 is carefully removed on one side, care being taken to avoid cutting 

 any large blood-vessels, for loss of blood would lower the excitability 

 of the spinal cord and obscure the dissection. For a similar reason 

 the medulla oblongata, which contains the vaso -motor centre, was 



