August 23, 1895.] 



SCIENCE. 



217 



actually carried out of the tissues upon the 

 free surfaces of the skin and mucous mem- 

 branes where, being ouiside of the bodj^, it 

 could no more interfere in any way with it. 

 But what was the fate of the leucocytes 

 that carried the lampblack out of the tis- 

 sues? They carry their load out and free 

 the body, but they themselves perish. 

 They sacrifice themselves for the rest of 

 the body as surely as ever did soldier or 

 philanthropist for the betterment or the 

 preservation of the state. 



Thus I have tried to sketch in briefest 

 outline some of the phenomena or processes 

 of life revealed by the microscope. Most 

 of those discussed have come under my 

 own personal observation and are there- 

 fore to me particularly real and instructive. 

 But to every one long familiar with the mi- 

 croscope and with the literature of biology, 

 many other examples will occur, some of 

 them even more striking. This discussion 

 has been confined to the above also because 

 it seems to me to show with great clearness 

 the way in which we can justifiably hope 

 to do fruitful work in the future. This sure 

 way it seems to me is the study of structure 

 and function together ; the function or ac- 

 tivity serving as a clue and stimulus to the 

 investigator for finding the mechanism 

 through which function is manifested and 

 thus give due significance to structural de- 

 tails which, without the hint from the func- 

 tion, might pass unnoticed. 



This kind of microscopical study, it seems 

 to me, may be well designated as Physiolog- 

 ical History. It is in sharp contrast with 

 ordinary histology, in which too often the 

 investigator knows nothing of the age, 

 state of digestion or of fasting, nervous ac- 

 tivity, rest or exhaustion. Indeed, in many 

 cases it is a source of congratulation if he 

 knows even the name of the animal from 

 which the tissue is derived. Such hap- 

 hazard observation has not in the past, and 

 is not likely in the future, to lead to splen- 



did results. If structure, as I most firmly 

 believe, is the material expression of func- 

 tion, and the sole purpose of the structure 

 is to form the vehicle of some physiological 

 action, then the structure can be trulj^ un- 

 derstood only when studied in action or 

 fixed and studied in the various phases of 

 action. 



Indeed, if one looks only for form or mor- 

 phology 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 con- 

 dition of fasting or digestion, he might find 

 the coarser anatomical peculiarities in each. 

 In all probability he would also find two 

 distinct structural types, with various grada- 

 tions. One tj'pe 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 indiscern- 

 ible. 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 different structural appear- 

 ances represent phases of activity, and all 

 might have come from the selfsame ani- 

 mal. In like manner, if certain parts of 



*Although in a different iield, the words of Oslborn 

 in discussing tlie unkno-mi 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 -n-ithin the 

 portals. Tlie 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 physiol- 

 ogist, ' armed with a microscope, ' I would like to 

 add " Am. Nat., May, 1895. 



