387 



with the differences which we may anticipate as existing between 

 the adult and the child at birth. This aspect of the problem illus- 

 trates, in a concrete form, the sort of question which is raised by 

 the anatomical study of the body during the period of growth. 

 The embryologists have worked out the formation and early devel- 

 opmental history of the various organs and parts of the human 

 body, but the study of the later fetal stages have been blocked by 

 the scarcity of material, and the inconvenience of dealing with it. 

 On the individual at birth, we have again more extensive observa- 

 tions, but for the period comprised between the first two years of 

 life and the age of twenty our information is again scanty. The 

 lower death-rate during this part of the life-cycle, as well as social 

 influences, combine to keep material between these ages out of the 

 dissecting-room. Here is an important part in the life-history of 

 man which needs to be investigated along many lines, and during 

 which it is most desirable to have a record of the changes in the 

 nervous system expressed in quantitative terms. In the general 

 problem which is here under discussion, our next step would be to 

 enumerate in man at birth the medullated nerve-fibres in the roots 

 of the spinal nerves. Such an enumeration will probably show us 

 between birth and maturity a very large addition to the number of 

 these fibres, but we still have to determine at what portion of the 

 period, and according to what laws this addition takes place. At 

 this point our observations on animals will assist us, and we should 

 certainly look for the occurrence of greatest addition during the 

 earlier part of the growing period. 



Let us assume, then, that we have obtained results which show 

 us the normal development of this portion of the nervous system 

 between birth and maturity. These observations could be used as 

 a standard. Once possessed of such a standard, we are prepared to 

 determine variations in the nature of excesses or deficiencies, and 

 in this instance the question of deficiencies is the one most easy to 

 handle. 



The studies of Dr. Hatai 1 on the partial starvation of white rats 

 during the growing period show that very definite changes can be 

 brought about in the nervous system when these animals are de- 

 prived of proteid food for several weeks. As a result of such treat- 

 ment, the total weight of the nervous system is reduced much 

 below that of the normal rat. Such a result, however, leaves two 

 points still undetermined: (1) the general nature of the changes 

 bringing about a diminution in weight, and (2) the parts of the 

 system in which changes occur. In testing our animal material by 

 quantitative methods, we should in the first instance direct attention 

 to a possible decrease or arrest of growth in the afferent system of 

 1 Hatai, American Journal of Physiology, 1904. 



