28 Edward F. Malone. 



by a definite type of cell character. That these two aspects of the func- 

 tion of the nervous system might be successfully studied in the hypothal- 

 amus by the use of experimental methods has been the controlling 

 factor in determining the nature of this article. 



But in addition to preparing a foundation for exj3erimental work an 

 attempt has been made to partially analyze the different elements in- 

 volved in the histological complex of each cell type and to note in 

 homologous cell groups of various animals what elements of cell charac- 

 ter are constant ; moreover in different cell groups of the same animal 

 those elements of the entire complex of cell character which are common 

 to the cells of two or more groups have been noted, and by this means an 

 attempt has been made to form a provisional, although crude, idea of the 

 degree of functional relationship among the different cell groups. At 

 first sight such an attempt might appear premature, or it might even 

 seem as though the task of the histologist were finished when he had 

 pointed out the existence and location of the various cell groups, and 

 that the determination of the functional relations of different cell groups 

 might be safely left to the experimental worker. Such a conclusion, 

 however, is not justified. Many regions of the brain are so complicated 

 as to make the results of experimental investigation extremely vague, 

 and in more suitable regions it is only under fortunate conditions that 

 we are informed of the functional relations of a cell group except that it 

 plays some unknown part in a complex mechanism underlying a com- 

 plex function. In solving the relations of the different components of 

 the various mechanisms of the nervous system histology must play an 

 important and perhaps the principal part, since in the nervous system, 

 as in the rest of the organism, it enables us to locate and to correctly 

 state the function of every cell group of one definite cell type, if the func- 

 tion of this cell type has in other cell groups been previously clearly 

 shown ; that, however, it is not self-sufficient is evident. 



But the neuro-histologist has a much more difficult task than that of 

 interpreting in a general way the differences and similarities of cell 

 character in different cell types. The cell types of certain cell groups 

 resemble one another through possessing certain features of cell char- 

 acter common to all, and on the other hand differ in respect to other 

 features of cell character; that such similarities and differences of cell 

 type are an indication of corresponding similarities and differences of 

 function I have already clearly shown in two cases. I have shown (Am. 

 Jour. Anat., 1913) that although the three different types of muscle are 



