ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 765 



they can be doubly stained without the least trouble. Dr. Gibbes has 

 not tried to do this against time, but has merely placed the sections 

 in the stain and allowed them to remain for some hours, and then 

 transferred them to methylated spirit, where they have been left as 

 long as the colour came out. In this way beautiful specimens have 

 been made, without the shrinking which always occurs in the nitric 

 acid process. 



Dr. Gibbes subsequently adds :* — " This process gives the most 

 satisfactory results, and the horrible nuisance of the nitric acid is 

 avoided. It brings out the bacilli quite as well as the other process, 

 and it stains all putrefactive bacteria and micrococci very deeply, so 

 that in the field of the Microscope blue micrococci and bacteria may 

 be compared with the red bacilli of tubercle. The stain can be used 

 cold equally well. The cover-glass in that case must be left in the 

 stain for at least half an hour." 



Grinding down a Slice of a Calcareous Fossil for Microscopical 

 Examination.f — Mr. H. J. Carter gives the following directions : — 



" Take about one part of half-dry Canada balsam, and place it on 

 the centre of a glass slide : heat it until melted over a spirit-lamp with 

 about half an inch vertical flame, moving the slide backwards and 

 forwards to prevent the latter from cracking ; add two parts of shellac ; 

 and when the whole has bubbled up, stir it with the point of a needle 

 so as to mix it well, and spread it altogether over a little more of the 

 glass than the size of the slice to be reduced. 



Previous to this, cut off with a watch-spring or very fine saw fixed 

 in an iron bow-frame (all of which may be obtained from an iron- 

 monger at a very small charge) the slice to be ground down ; and if 

 there be much siliceous matter in the fossil, the saw (which is very 

 cheap) may be sacrificed by the addition of emery powder and water 

 to the groove, as this accelerates the cutting. (Of course where a 

 machine with horizontal turning-wheel is possessed, such as is used 

 for cutting siliceous fossils, flints, &c., this is the quickest and most 

 economical way to obtain the 'slice.') 



Having thus obtained it, so far prepared, rub one side (viz. that to 

 be examined) down to scratchless smoothness on a schoolboy's slate or 

 very fine honestone with level surface, to effect which it is absolutely 

 necessary that all the materials should be entirely freed, by washing, 

 from every particle of emery or siliceous mineral that may happen to 

 be present, otherwise the calcareous surface will become almost irre- 

 mediably furrowed. 



Next dry the slice on a tin or paper tray placed inside the fender 

 by the fire, where it can remain until the next part of the process is 

 completed. 



Now remelt the material on the glass slide as before, and when 

 sufficiently fluidified to present a uniformly level surface (but not burnt, 

 for this would destroy the tenacity of the cement, and thus give it a 

 crispness which, by cracking, would defeat all attempts at further 



* ' Practical Histology and Pathology,' 2ncl eel., 1883, p. 142. 

 t Ann. and Mag. Nat. Hist., xli. (1883) pp. 29-30. 

 Ser. 2.— Vol. ni. 3 E 



