960 SUMMARY OF CURRENT RESEARCHES RELATING TO 



centre of the plate, whatever the position of the jaws, and they being 

 always equidistant from the centre, it follows that the slide, when 

 clasped between them, must be perfectly centered. For the purpose 

 of retouching old slides the ordinary spring clips are retained. 



An improvement has been made in the supporting stand, the iron 

 tripod being now so arranged that the hind legs are removable and, 

 being held in position by a clamp-screw, the same screw serves to 

 clamp the instrument upon the edge of the work-table, should this 

 mode of using it be preferred. 



New Process for Preparing the Brain.* — In place of nitric acid, 

 chloride of zinc or chloral, a new process is described by which the 

 brain is plunged in a saturated solution of bichromate of potass in a 

 vessel large enough to admit of complete submersion, or if it be wanted 

 for histological studies, susceptible of being cut in small slices for 

 microscopical examination, bichromate of ammonia should be sub- 

 stituted for bichromate of potass. The brain should remain immersed 

 a fortnight or longer ; it will then be much swollen, and the infiltra- 

 tion will be completed. It is then taken out of the bath and plunged 

 into simple water, in order to expel any excess of the bichromate. It 

 is then placed in a bath of carbolic acid, 25 grammes to 1000 grammes. 

 This process has the property of hardening the brain-substance, and 

 reducing it almost to its normal size. A little acid must be added 

 from time to time in order to keep up its hardening effect, which is 

 apt to lessen. Six to ten days will suffice for its remaining in the 

 acid bath. 



As soon as the brain is taken out of the carbolic acid bath, it is 

 plunged into a bath of pure glycerine for three or four days ; the 

 specimen may be wrapped in a cloth so as to prevent any part of the 

 brain from emerging from the ambient liquid. It should not be left 

 longer in the glycerine, for the brain absorbs a very large quantity of 

 it, which might interfere with the hardening process. The brain is 

 then taken out, placed on the flat side on soft linen, and exposed to 

 the air. Should there be an excess of glycerine, plunge it for eight 

 to ten minutes in a water bath. It is left now to itself, and will 

 assume a green bronze colour, dry, and mummify almost insensibly. 

 In two or three weeks the desiccative process will be completed. The 

 specimens can be kept in open air or in boxes. 



This process of preserving the brain, though seemingly com- 

 plicated, is in reality very simple, if once the habit of using it be 

 acquii'ed. Such brains have now been in the laboratory for two years 

 and a half, completely imputrescible, and have lost only three-tenths 

 of their original value. They are susceptible of being freely sliced for 

 histological investigation. 



Action of Concentrated Osmic Acid on Bone-cells.t — M. F. 

 Tourneux has studied the exact form and intimate relations of the 

 osteoblast by the combined action of impregnation of the tissue with 

 concentrated osmic acid, and decalcification by the aid of formic acid 



* Lond. Med. Eec, Aug. 15, 1881, pp. 308-9. 

 t Bull. Sci. Dep. Nord, iv. (1881) pp. 113-15. 



