1895.J MICROSCOPICAL JOURNAL. 309 



Indeed, if oue looks only for form or morphology in 

 the study of histology, the very pith and marrow is 

 more than likely to be lost.* 



For example, if one wished to study the comparative 

 histology of the pancreas and were to take pieces from 

 various animals to be compared without regard to their 

 condition of fasting or digestion, he might find the 

 coarser anatomical peculiarities in each. lu all prob- 

 ability he would also find two distinct structural types, 

 with various gradations. One type with clearly defined 

 cells and nuclei, the other with the cells clouded, filled 

 with granules and with the outlines of cells and their 

 nuclei almost indiscernable. Between these there might 

 be various gradations in the different forms. And yet, 

 from what has been stated above, it is plain that all 

 these difi'erent structural appearances represent phases 

 of activity, and all might have come from the selfsame 

 animal. In like manner, if certain parts of the nervous sys- 

 tem were to be studied comparatively, and the tissue taken 

 from one animal after refreshing sleep and rest, from 

 another after exhausting labor, another in infancy, and 

 another from an animal decrepit in years, the difference 

 in general appearance and in structural details would be 

 striking enough to satisfy any morphologist that, as with 

 the structure of the pancreatic cells, there were two or 

 more distinct types ; but the physiological histologist 



*Althoiigh in a different field, the words of Osborn in discussing the un- 

 known factors of evolution are so pertinent that they may well be quoted : 

 "My last word is that we are entering the threshold of the evolution problem, 

 instead of standing within the portals. The hardest tasks lie before us, not 

 behind us." '"We are far from finally testing or dismissing these old factors 

 [of evolution], but the reaction from speculation upon them is in itself a 

 silent admission that we must reach out for some unknown quantity. If such 

 does exist there is little hope that we shall discover it except by the most 

 laborious research ; and while we may predict that conclusive evidence of its 

 existence will be found in morphology, it is safe to add that the fortunate 

 discoverer will be a physiologist, 'armed with a microscope,' I would like to 

 add."— ylm. Nat., May, 1S95. 



