616 RECOKD OF CURRENT RESEARCHES RELATING TO 



four hours in equal parts of metliylated alcohol and water, had been 

 kei>t sixteen months in glycerine.* 



Preparation of Diatoms in situ : means of avoiding Air- 

 bubbles. f — M. Petit, referring to the process of Brebisson of preparing 

 Odontidium Tabellaria, viz. by placing the filaments on thin glass 

 or mica, and heating on a plate of platinum, says that this presents 

 serious difficulties to amateurs who regard the beauty and cleanness 

 of their preparations. In the first place, it is rare tliat we are able 

 to carry the calcining sufficiently far to completely destroy the cel- 

 lulose, which reduced simply to charcoal blackens the frustules ; 

 secondly, preparations thus calcined are with difficulty penetrated by 

 Canada balsam, even although care may have been taken to make it 

 sufficiently fluid by the addition of an essential oil, &c. ; thirdly, in 

 calcining on the cover-glass only one of the faces of the diatom is 

 ordinarily seen, whilst it is often essential in determining the 

 species to see the two aspects. 



He therefore proposes the following method to get rid of these 

 inconveniences. He places the diatoms (previously washed in fresh 

 water if they are marine) in concentrated cold nitric acid for twelve 

 hours ; this time is sufficient to " nitrify " the cellulose, without destroy- 

 ing it or dislocating the filaments After sufficient washing, they are 

 j)laced on the cover-glass, and calcined to a red heat on a plate of 

 platinum until the deposit has become white ; it is then easy to make 

 dry preparations in which there is no deposit of charcoal ; for in this 

 case the cellulose, owing to the action of the nitric acid, is destroyed 

 without aiii)reciable residue. 



To avoid bubbles of air with Canada balsam, he makes use of oil 

 of lavender, jjlacing a small drop, after the calcination and when the 

 preparations have got cold, on the cover-glass ; this infiltrates into 

 all the cavities, and facilitates the penetration of the balsam. The 

 cover-glass should then be j^laced on a drop of balsam deposited on 

 the elide, and heat applied with a spirit lamjj, so as to di'ive away the 

 oil of lavender and to evaporate a part of the balsam. 



In order to ijrejjare diatoms in situ in their various aspects on one 

 slide, he boils about the third part of the collection, and mixes this, 

 after washing, with the two other parts, treated with cold nitric acid 

 as above mentioned, and thus obtains excellent preparations containing 

 both diatoms m situ and those separated, which is of great advantage 

 for study. 



Mechanical Turntables,^ — Mr. Spencer Eolfe, referring to Mr. 

 Rogers' electrical mounting table,§ says that some time since he 



* The method is one tliat rniglit be used for the examination of the retina of 

 rare animals when the eyes have to be procured from a distance. After the 

 remarkable observation of the anastomosis of the ganglion cells of the elephant's 

 retina by Corti, to which there has been as yet no parallel, a further examination 

 of the retina of that animal is very deskable. The eyes of elephants in a condi- 

 tion suitable for such an examination are not easily procurable, but by the use 

 of the above method available specimens might be had from India. 



t ' Brebissonia,' i. (1879) p. 121. % ' English Mechanic,' xxix. (1879) p. 139. 



§ This Journal, ii. (1879) p. 4G9. 



