PROBLEMS IN HUMAN ANATOMY 385 



are compared, it is found that the increase in the brain-weight fol- 

 lows quite another law, and that in this latter case it is relatively 

 much less marked than in the former. This result at once suggests 

 that the mechanism of the increase is dissimilar in the two cases. 

 For the solution of the problems that are raised by such investi- 

 gations as those just cited, we need to employ quantitative methods, 

 and on this topic a word is here in place. 



Microscopic anatomy and histology, like all the sciences, have 

 passed through a series of phases which are as necessarily a part of 

 their history as birth, growth, and maturity are a part of the life- 

 history of a mammal. The microscope in its early days enabled 

 Schwann to propound the fruitful theory that the tissues were 

 composed of cells. A preliminary survey showed that these cells 

 were different in their form and arrangement in the different parts 

 of the body, and a still more careful examination with the aid of 

 various dyes or solutions altering the tissues in a differential way 

 gave the basis for yet finer distinctions. This phase in the develop- 

 ment of the science, however, may be fairly compared with quali- 

 tative work in chemistry, where the object is to determine how 

 many different substances are presented in the sample examined. 

 Naturally, the next step is the introduction of quantitative methods, 

 and we are, therefore, now using the methods of weighing, measur- 

 ing, and counting for the purpose of rendering our notions more 

 precise, and thereby facilitating accurate comparisons. When 

 emphasizing this point, we do not, however, forget that hand in 

 hand with this quantitative work the qualitative tests have been 

 marvelously refined, and that these necessarily form the foundation 

 for quantitative work, since all such work must deal with the ele- 

 ments or groups of elements which can be sharply defined, and the 

 basis for their definition is given through qualitative studies. As 

 progress is made along these lines, we appreciate more and more 

 that it is of importance for us to know not only how much brain 

 and how much spinal cord by weight normally belong to a given 

 species of animal, but also the quantitative relations of the different 

 groups and classes of elements which compose these parts. We are 

 continually asking ourselves how far the range in gross weight of the 

 central nervous system may be dependent on changes in the number 

 of elements in the different divisions or localities, and how far 

 dependent on the mere increase in the bulk of the individual units 

 without any change either in their absolute number or relative size. 

 Work along this line rests as we know on the neurone theory, that 

 epoch-making generalization concerning the structure of the nerv- 

 ous system which was put forward by our honored colleague 

 Professor Waldeyer. 1 Most of us are aware that, at the moment 

 1 Waldeyer, Deutsche medidnische Wochenschrift, 1891. 



