770 SUMMABY OF CURRENT RESEARCHES RELATING TO 



this use is now developed, differentiate the various tissues from one 

 another, and are a most invaluable help to exact knowledge. As the 

 presents of sword and spear and shield, offered, along with the jewelry 

 and costly robes, to the daughters of Lycomedes, by the crafty 

 Ulysses, in the old Homeric story, served to discover the yoimg 

 Achilles in spite of his womanly disguise, so do these chemical 

 staining fluids serve to disclose to us by their selective power the 

 different tissues and organs in substances otherwise alike transparent 

 and invisible. The various aniline colours with which chemistry has 

 enriched the world, transforming a waste product from a nuisance to 

 a source of wealth, have given a new and almost inexhaustible apparatus 

 of verification to the microscopist. But perhaps a still more im- 

 portant means of verification is to be found. 



5. Improved Lenses and Accessory Apparatus. — Abbe's introduc- 

 tion of the homogeneous immersion system of objectives, and the 

 greatly increased aperture which at once resulted, and the more 

 perfect adjustment by motion of the inner system of lenses of the 

 objective as designed by ToUes, mark an era in the history of the 

 Microscope and afford a new and powerful adjunct to the verification 

 of former discovery. And this is being done. Dr. W. B. Carpenter, 

 in his Montreal address last year, somewhat loftily asserted that we 

 in America were, in the matter of wide aperture, simply going over 

 the track which the English microscopists traversed twenty-five years 

 ago, and have now abandoned. The statement is wide of the mark in its 

 literal meaning. If any English microscopists had dry 4-lOths of 110° 

 or glycerine immersions 1-Gth of 130° balsam angle twenty-five years 

 ago they were strangely reticent about them. But in another sense 

 his words are most true. American microscopists are traversing again 

 the ground passed over twenty-five years ago, that the observations 

 made then with inferior lenses may be corrected and verified by the 

 superb glasses of to-day. But Americans are not alone in this. 

 English and Continental scholars are enlisted in the same work, and a 

 London optician leads the world in making lenses of wide aperture. 

 Let me not be understood, however, as claiming all perfection for all 

 uses for the wide-angled lenses. The views of Prof. Abbe in regard 

 to the limitations of wide apertures seem to me eminently just. But 

 not alone in the objective do we find means of more accurately testing 

 our observations. Many improvements in the accessory apparatus are 

 of great value. 



6. A Better Knowledge of Optics. — This is perhaps the most 

 important of all means of verification of microscopic observations. 

 Without this all the rest will be in vain. We must elaborate 

 or the simplest apparatus will yield no real gain of knowledge 

 to the world unless the eye be trained to comprehend what it 

 sees, to interpret the appearances that present themselves and dis- 

 criminate the causes that produce them, and so trace back the effects 

 of the lenses themselves, of the diaphragm, of the obliquity of the 

 light, and the effects due to the real structure of the object under 

 examination. The mathematical reasonings of Helmholtz and still 

 more those of Abbe on the true theory of microscopic vision may not 



