430 HENRY H. DONALDSON 



monstrously developed. Thus there are forms depending mainly 

 on the sense of smell or of taste or touch or vision and in each 

 instance showing a relative over-development of the neural 

 structures concerned. The study of these and other instances 

 of unbalanced structure has furnished a clue to the significance 

 of various cell groups in the human bulb otherwise difficult to 

 interpret. For example it has thus been possible to clear up 

 the arrangement of the nuclei of the vestibular apparatus — from 

 which the cerebellum has been elaborated, and also to interpret 

 such a cell group as the nucleus of the fasciculus solitarius, the 

 center of the taste (p. 234). But the applications of these com- 

 parative studies extend still farther. By their aid it is possible 

 to distinguish between the primitive thalamus (paleothalamus) 

 and the large additional mass (neothalamus), as it appears in 

 man and the anthropoids, with its various cell groups and highly 

 elaborated cortical connections. Using like methods it has been 

 possible also to follow the evolution of the neopallium or the 

 part of the cortex (pallium) superadded to that primitively 

 associated with the olfactory apparatus. 



In dealing with the functional problems the general somatic 

 sensations have received careful consideration and the results 

 obtained by Head and his collaborators have been incorporated. 

 Of special interest in this connection is the problem of the media- 

 tion of pain. The questions here are many. Are there special 

 afferent nerve fibers for pain only, or do some terminals of these 

 somatic fibers yield sensations of pain while other terminals of 

 the same fibers mediate different sensations, or can over-stimu- 

 lation of any of these fibers give rise to sensations of pain? Our 

 author discusses these questions and concludes that there may 

 possibly be some special pain nerves, but also that " most sensory 

 nerves may upon occasion function as pain nerves." 



The questions here put in connection with nerves mediating 

 pain, may be equally well asked with regard to the other 

 sensory nerves and they serve to raise the ghost of the doc- 

 trine of specific energies. Although it is not much discussed, 

 and is usually criticized adversely, the doctrine of the specific 

 energies of nerves still casts its shadow over neurology. The 

 rigid form of this doctrine, the form with which Helmholtz 

 worked, looks upon the sensory nerve fiber as an unbranched 

 thread running from its peripheral termination, where to be 



