2 NERVOUS SYSTEM OF VERTEBRATES. 



of nervous structures, the statement of problems and the planning 

 of investigations for their solution gain most from more general 

 considerations of function, namely, considerations of the conditions 

 and mode of Hfe of the organism. 



x^NATOMiCAL METHODS. — ^Thc method by which the study of the 

 nervous system was first undertaken is also the first to be used by 

 the student of today, namely, dissection. The purpose of dissec- 

 tion is to show the general place relations of the parts of the nervous 

 system to other organs and the apparent structural connections 

 between the two. Even to the investigator of original problems 

 the method is still useful, and as it must be practiced in preparation 

 for physiological experimentation and operation for the study of 

 degeneration phenomena, the importance of thorough training 

 in dissection can scarcely be over-estimated. The refinement of 

 dissecting microscopes and mechanical appliances in recent years 

 has made dissection appHcable to more and more minute objects 

 and at the same time has extended its usefulness to problems, 

 which could be approached before only by more indirect and 

 tedious methods. The great advantage of handling one's object 

 and of seeing its parts in their three dimensions makes the method 

 of dissection indispensable and warrants every efi'ort to refine 

 and extend it. 



When the dissection of the nervous system had reached the 

 height of its efficiency by the appliances knowTi to the earHer 

 workers, as in the studies of the nerves of fishes by Stannius, the 

 introduction of the microtome and the method of studying sections 

 opened the way for great advances especially in the study of the 

 central nervous system and of development. When the sections 

 were stained by carmine or ha^matoxylin, more or less complete 

 pictures were obtained of the structures in each section. By 

 carefully keeping all the sections into which an object might be 

 cut and mounting them in their serial order, it became possible 

 to find the limits and form of structures too small to be dissected 

 and to trace bundles of fibers from section to section throughout 

 their course. Although for special investigations this method is 

 largely replaced by more exact methods, it is still useful for the 

 study of the general morphology of the nervous system and the 



