1884.] 



MICEOSCOPICAL JOURNAL. 



191 



subject -within a very recent period, 

 that it may be said that a new art has 

 been developed which we may call 

 microtomy. 



In working with vertebrate mate- 

 rials- hardening and killing should 

 be done in such a way as not to dis- 

 toil the axis of the embryos, in order 

 that the knife and microtone may be 

 adjusted so as to cut in any desired 

 plane with accuracy. The embed- 

 ding must be as homogeneous as 

 possible ; for this purpose saturating 

 the object with paraffin has been 

 found to be the best, so that evenly 

 thin sections may be produced. The 

 methods of Biitschli, Plateau, Cal- 

 berta, Duvall, all sei've this purpose, 

 and their relative values are probably 

 expressed in about the order in which 

 they stand. Staining is best accom- 

 plished in embryological work by 

 dyeing the object as a whole ; this 

 saves time and may be done in a num- 

 ber of ways. Mounting should be 

 done serially and with the ribbon 

 method ; where hard paraffin is used, 

 the sections are rapidly and easily laid 

 on the slide with needles in neat order, 

 if the fixing is done with a compound 

 of clove oil 3 volumes and collodion 

 I volume, which is thinly painted on 

 the slide, and on which the sections 

 are carefully laid, when the slide may 

 be gently warmed for a minute ; this 

 melts the paraffin in the sections, the 

 clove oil is driven off, and the sections 

 fixed by the collodion, when a few 

 drops of turpentite will immediately 

 dissolve and remove the included and 

 adherent paraffin, when the mounting 

 may be done under an oblong cover 

 in balsam. 



These methods enable the student 

 to interpret the structure of an or- 

 ganic body in three dimensions, and 

 so great an accuracy of preparation 

 is thus attainable that enlarged models 

 are easily made from super-imposed 

 card or wax plates joined together 

 and cut from outlines drawn by the 

 help of the cameralucida from the 

 successive sections enlarged to a com- 

 inon scale ; or it is even possible in 



the same manner to construct stereo- 

 grams by drawing camera outlines 

 one upon the other, for the reason 

 that if the sections are properly pre- 

 pared, every part will be in its proper 

 place and the final result will be ac- 

 curate. In this way I have built up 

 views of embryo fish crania in per- 

 spective from one side ; cartilaginous 

 ci'ania, which it would be utterly im- 

 possible to clean on account of their 

 small size, so as to make an entirely 

 sei^viceable preparation, because or- 

 dinary methods of preparing would 

 inevitably show impoi'tant parts out 

 of place and render the object unre- 

 liable for the purpose of illustration. 



Recent Studies on the Theory of 

 the Microscope and their Prac- 

 tical Results as Regards the Use 

 of the Microscope in Scientific 

 Investigations.* 



Few who are not constant readers 

 of the literature pertaining to the 

 physics of the microscope are aware 

 of the great advances that have been 

 made in the knowledge of the micro- 

 scope as a physical instrument, and 

 of the correspondingly great progress 

 in the construction of the optical part 

 due to such knowledge, that has been 

 made within the last ten years. Never- 

 theless, the subject is of great impor- 

 tance to every observer, and although 

 to make it clearly understood it should 

 be treated mathematically, in a man- 

 ner which the author of this paper 

 would not undertake, it has seemed 

 desirable to present the salient features 

 of our knowledge of the microscope 

 as a physical instrument, in a manner 

 to indicate fairly well the bearing of 

 recent researches upon the scientific 

 use of the instrument. To do this, 

 for the benefit of the biologist, histolo- 

 gist, and others whose time and in- 

 terests have been too much occupied 

 with their work to study the merits 

 of different objectives and accessories, 

 makes it advisable that we should 



* Read before Section G, A. A. A. S. 



