310 PHYSIOLOGY CHAP. 



In order to obtain a more constant and readily measurable 

 stimulus, Coenen has tested Langelaan's discovery by means of 

 an Erb's electrode with three seconds application of weak induced 

 currents. In an area limited to the ulnar surface of the forearm 

 he showed that the skin is more sensitive near the axis of the 

 limb, and that the subject felt pain here with a current that was 

 unperceived in the neighbouring regions. 



VI. As was stated above, the real and perfect metamerism 

 of the spinal roots is only seen in the segmental arrangement of 

 the cell columns of the ventral horn of grey matter. This fact 

 fully bears out the physiological view that the spinal cord 

 represents a series of central organs (myelomeres), which are 

 intimately connected, and are more or less unitary in their 

 functions. 



The predominating function of the myelomeres is "reflex 

 activity." This term, borrowed from the physicist who speaks 

 of the reflection of light and heat rays corresponds ill with the 

 physiological phenomena which it is intended to connote. In 

 the widest sense any immediate reaction of a living and excitable 

 element to an external stimulus may be called a reflex act. In 

 a narrower sense, however, as applied to the nervous system, 

 the reflex act is the involuntary transformation of a centripetal 

 into a centrifugal nerve impulse, by means of a central organ, 

 represented by a group of ganglion cells. We say " involuntary 

 transformation " to distinguish the reflex act from the voluntary 

 act, which may also follow on, and be evoked by, an afferent 

 impulse. 



Typical examples of common reflex actions are : sneezing on 

 stimulation of the nerves of the nasal mucosa, coughing from 

 stimulation of the glottis, swallowing from contact of fluids or 

 solids with the isthmus of the fauces, contraction of the pupil 

 to light, movements of the arm or leg on tickling the armpit or 

 sole of the foot, etc. Every one knows that these movements are 

 involuntary for although the will can check them to a certain 

 extent, it cannot inhibit them and that they may be conscious 

 or unconscious, since they may occur in the waking or the 

 sleeping state. 



But in experiments upon animals it is difficult to distinguish 

 " reflex " acts from the " voluntary " acts which result from 

 conscious sensations. In order to establish the purely reflex 

 nature of spinal acts the influence of the will is cut out in 

 animals, either by narcosis, or by decapitation or removal of the 

 cerebrum. None of these methods, however, seem to us adequate. 



The first method is founded on the fact that narcotics (opium, 

 chloroform, ether) suspend the psychical activities first, without 

 loss of excitability or conductivity in the lower nervous elements. 

 But according to the best auto-observations in chloroform narcosis, 



