45 



ADVANTAGES OF PHOTOMICROGRAPHY. 



Oue great advantage of photomicrography is that it leads to the prep- 

 aration of better microscopic slides, because, in part, of the rule that does 

 not permit the negative to be altered in its material parts; in part also 

 because the damaging defect can not always be removed. Another ad- 

 vantage is that when correctly carried out it can tell nothing but the truth 

 with reference to the parts in focus. It is maintained by good authority 

 that it sometimes reveals things not visible to ordinary vision. I have 

 often seen things in photomicrographs that had escaped my attenl;iou 

 before, but always when I came to observe carefully again I was able 

 to see them. A skillfully prepared photomicrograph shows details more 

 distinctly, with greater conti'ast, than they have when one observes 

 them through the microscope; I see no reason wliy if the proper conditions 

 were at hand it may not reveal details beyond the reach of ordinary micro- 

 scopic vision. A sensitive plate is not blinded by light or tired with long 

 looking. Photomicrography is not here presented as a remedy for all 

 ills; drawings have certain advantages; but every one can not draw, and 

 careful drawings require much more time than photomicrography. The 

 best of both is had when the details of photomicrography are supple- 

 mented by a consti'uctive diagi'am which uites all in one. 



In science teaching pliotomicrography fills a place that nothing else 

 can. Few people comparatively ever use the microscope to any educa- 

 tional pui'pose; probably not more than a tenth of the students in our 

 colleges and universities are familiar with anything more than Its simplest 

 revelations; popular courses are wanted in and out of the colleges; psy- 

 chology, pedagogy, child study, and all organic studies call for illustra- 

 tions of biological laws or histological relationships which concern them; 

 for most of them it is photomicrography or drawings or both or nothing; 

 and no one that has ever tried it will hesitate for a moment to say that 

 the photomicrography must not be left out; it makes things real in a way 

 that a diagram can not; it helps the interest, not indeed to the same 

 extent that the microscope does, but to something like the same extent 

 that the microscope would, if the student did not prepare his own object 

 and if all the students could see the same thing at the same time through 

 it and have the view explained while looking. I am sure that the histo- 

 logical lantern slide is with us to stay, and that the histological half-tone 

 shortly will be. 



