92 



THE AMEEICAN MONTHLY 



[May, 



lief that the nuclei are either one 

 homogeneous mass, or a collection 

 of bioplasmic granules. 



But neither view is correct. 



"When we apply the new -^ of 

 over 120° interior angle, taken in a 

 medium of 1.525 index as used by 

 Mr. ToUes for measurement, rather 

 than a medium of 1 .50 index, which 

 latter would give several degrees 

 more angle to the objective, our 

 error of observation in the first 

 trial is wonderfully conspicuous ; 

 and this performance of the high 

 angle water-lens is noticeably out- 

 done. 



We now begin to obtain some 

 accurate idea of the arrangement 

 of the bioplasm in the nuclei of 

 the living, growing epithelial cells 

 of the newt, as well as of rapidly 

 developing nuclei in various parts 

 of other animals. 



For want of an engraving the 

 reader is referred, if not already 

 familiar with the subject, to an ar- 

 ticle by Dr. Klein, in the London 

 Quar. Jour, of Microscopical 

 Science for July, 1879, describing 

 and illustrating the nuclei of the 

 newt, as studied by him with the 

 new Zeiss high angle ^g- and ^^-inch 

 oil-immersion objectives, which ar- 

 ticle led me to make the prepara- 

 tions I now have. What would be 

 much better for the student, would 

 be to get one of Tolles' new ^-inch 

 objectives, and prepare and study 

 these difficult objects for himself. 

 It is only necessary to immerse the 

 living tissue in a weak solution of 

 picric acid for a few days, then 

 thoroughly wash, transfer to, and 

 harden in, alcohol ; cut the sections 

 very thin, stain with carmine, and 

 mount in Canada balsam. 



With a ^0" like the one above re- 

 ferred to, and a Tolles' one-inch of 

 30°, the histological or biological 

 student would have the ne 'plus 

 ultra of optical appliances for his 



study. The one-inch is constructed 

 with eight lenses, has a very flat 

 field, and its defining and resolving 

 power, as well as penetration, are 

 beyond criticism. It easily resolves 

 40,000 lines to the inch, bears high 

 eye-piecing, and is to my mind the 

 best lens the student of histology 

 can use for a low power for general 

 examinations. 



The ^Vj with its maximum angle, 

 works easily through -gV-inch covers 

 and can be used as a water, glycer- 

 in, or homogeneous-immersion at 

 pleasure, by means of collar-adjust- 

 ment, and gives fair results worked 

 dry. Mr. Tolles' idea of retaining 

 the screw-collar is, to my mind, one 

 of the best features of his new 

 production. 



The reason for this is, that it 

 affords a means of using water as 

 an immersion medium when one is 

 mounting several preparations, or a 

 number of slides of one kind, and 

 desires to make a cursory examina- 

 tion of them at once with high 

 powers before any change shall 

 have taken place, and without wait- 

 ing for covers to become fixed by 

 hardening of the balsam. 



The medium I have found best 

 for homogeneous-immersion, and 

 one that I believe will come into 

 general favor, is glycerin brought 

 up to the required index, by making 

 a saturated solution with it and 

 sulpho-carbolate of zinc. Chloride 

 of cadmium has also been recom- 

 mended with glycerin. The for- 

 mer medium is neat ; and as yet 

 I have found but one objection, 

 and that not a serious one, to its 

 every-day use, viz. : it is just a little 

 too thick. When the new yV is used 

 for homogeneous immersion, the 

 systems are closed and no attention 

 is given to the collar-adjustment 

 unless great accuracy is required, 

 and we desire to adjust for the 

 length of the microscope-tube. 



