266 The Microscope. 



nucleoli, which are small albuminoid masses containing plastin, 

 not stained hy methyl green, and not dissolved by the dissolvents 

 of nuclein. Third, mixed nucleoli, consisting of both nuclein 

 and albuminoid substances, which however remain separate, as 

 methyl green will stain one portion without affecting the other. 

 Fourth, nucleolo-nuclei or minature nuclei, which are made up 

 of the same elements as the nucleus itself, possessing, there- 

 fore, a membrane, a protoplastic portion and a nuclein tubule. 

 Such nucleolo-nuclei may be found in cells of the Lithohius. 

 Mixed nucleoli are probably only nucleolo-nuclei devoid of a 

 proper membrane. 



THE SHORT SLIDE AS A SAFETY SLIDE. 



DR. HENRY SHIMER. 



MUCH has been said in microscopical books, journals and 

 elsewhere about care in using high power objectives, and 

 warning of the danger of racking downward, etc. Having to 

 use a fine, high power, dry objective of very short working dis- 

 tance, always nearly or quite touching the cover glass when in 

 focus, it is well known that the thickness of a series of cover 

 glasses of the same number varies greatlj'^ ; hence, one of a pack- 

 age could be worked through while another could not. 



Looking across the stage and carefully racking down until 

 the front of the lens was so close to the cover that I could not 

 see between them with a hand lens, thereupon applying the 

 eye to the eye-piece and manipulating the screw of the fine 

 adjustment, I often found that I was still above the focus, and 

 it became an important consideration as to how close I could 

 press the cover glass with safety and advantage when searching 

 for an object mounted in aqueous or glycerine medium. The 

 little accidental motes when seen moving about in the medium, 

 sounded a note of alarm and said: *' You can go no closer ; even 

 now there is danger." I have a so-called safety nose-piece in 

 my possession, a contrivance with a spring in it between the 

 tube and the objective, to prevent unbearable pressure, but it is 

 not always on the stand ; moreover, it is a troublesome thing in 

 changing objectives where the stand has a short working dis- 

 tance, for it makes quite a long affair to handle and not touch 



