2G4 SUMMARY OF CURRENT RESEARCHES RELATING TO 



equally circular figure. This difficulty is usually surmountable by 

 examining the wet surface of the grinding at intervals with a hand lens. 

 When doubt still exists the only sure method is to grind the calculus in 

 t wo planes, at right angles to each other, so as to obtain a sector con- 

 sisting of a fourth of the whole ; the centre can then be determined by 

 its exposure in both planes. 



After the process is completed, the ground surface is carefully washed 

 and cleared of debris by allowing water to drop from a height through a 

 cone of filter paper ; the half of the calculus so prepared is excluded 

 from dust and allowed to dry. It is, in the next place, cemented to a 

 slide with solid Canada balsam, a fragment of which is heated on the 

 slide over a spirit lamp until it melts; and in order to diminish the 

 brittleness of the balsam, a small quantity of the ordinary mounting 

 solution in xylol is first placed on the slide, the materials being mixed 

 after heating by rocking the latter to and fro. The half of the calculus 

 is now placed on the slide, the central portion of which is already covered 

 with the melted balsam. A copious effervescence takes place from the 

 under side of the calculus, owing to the expansion of the air in its 

 interstices. The slide must now be turned over, so that the ground 

 surface can be viewed, the calculus being moved about and gently pressed 

 until no trace of air remains between the specimen and the glass. As 

 soon as the balsam has set, the material is ground away from the convex 

 side until the chief bulk has been removed. The last and most delicate 

 part of the process is the grinding of the section to such a degree of 

 thinness as to allow the light to pass through it. This is done, first on 

 fine glass-paper, but completed on the hone with water. When the 

 requisite thinness is reached, the surface is washed by allowing water to 

 drop on to it through a cone of filter paper ; lastly, when the section is 

 dry, a xylol solution of balsam is placed on it and the cover-glass applied. 



Caffyn, C. H. — A Rock-grinding Machine for Amateurs. 



[Describes how to adapt a sewing-machine for making petrological sections 

 and the method of preparation of a rock section.] 



Knowledge, xxxiv. (1911) pp. 10-11 (3 figs.) ; pp. 74-5. 



(4) Staining and Injecting:. 



Staining Blood-films.* — J. Sabrazes uses an aqueous solution 

 of medicinal methylen-blue in dilutions of from 1 : ; J >00 to 1 : 1000, 

 customarily 1 : 500. Only the supernatant fluid is employed, and this 

 is removed by means of a capillary pipette. The film must be well dried 

 and fixed with osmic acid paper. The films may be counterstained with 

 eosin. The eosin solution is made by mixing 5 c.cm. of a saturated 

 solution of eosin (francaise pure) in 95 p.c. alcohol with 10 c.cm. of 95 p.c. 

 alcohol. 



Demonstrating the Presence of Mitochondria in Cartilage-cells.f 

 J. Renaut removes cartilage from the long bones of foetal sheep as soon 



* C.R. Soc. Biol. Paris, lxx. (1911) pp. 247-8. 

 t Comptes Rendus, clii. (1911) pp. 536-8 (2 figs.). 



