540 SUMMARY OF CURRENT RESEARCHES RELATING TO 



slides with their smooth edges parallel with the edges of the wedge- 

 shaped cut. 



For the ordinary rapid examination of vegetable tissues, the 

 specimen is held gently in the opening by the thumb of the left hand, 

 while the razor dipped in alcohol is drawn steadily over the glass 

 slips towards the apex of the wedge, with the cutting edge held at 

 the usual angle. After the first cut, if uniformity in the thinness of 

 the sections is not necessary, the object can be simply advanced 

 slightly by the hand, and after a few trials it will be found that 

 really thin sections can easily be made in this simple way. 



When, however, it is necessary to have sections of extreme or 

 uniform thinness, it is best to screw across the under side of the 

 block a strip through which a thumb-screw with fine thread is fitted 

 to work. By this means the object can be raised regularly any desired 

 distance at each cutting. 



The block can be prepared in a few minutes by any one, and with 

 all ordinary vegetable tissues very satisfactory sections can be cut. 

 Hard wood cannot be cut safely in a section-cutter without being first 

 soaked or steamed, and as a keen-edged plane will cut beautiful 

 sections quickly and easily, it is best to cut such wood in that way. 

 Sections of different kinds of wood can be cut at the same time by 

 screwing small blocks of each together and taking a section of all at 

 one stroke of the plane. 



Natural Injection of Leeches.* — Dr. C. 0. Whitman has often 

 noticed that leeches hardened in weak chromic acid, or in any chromic 

 solution, are beautifully and naturally injected with their own blood. 

 Where the circulatory system is to be studied by means of sections, 

 this method seems to be the simplest and most reliable one. Not only 

 the large:^ sinuses, but the intra-epithelial capillaries may be easily 

 traced by this method, as was first pointed out by Prof. E. E. 

 Lankester.| 



Methods of Injecting Annelids. J — For annelids with dark tissues 

 like Hirudo, M. M. Jaquet recommends that a light-coloured (white or 

 yellow) injection-mass should be employed, while for transparent 

 animals dark colours are preferable. Chrome yellow serves as a good 

 colouring substance. It is easily obtained by mixing solutions of 

 bichromate of potassium and acetate of lead. A copious yellow pre- 

 cipitate is formed, which should be washed on the filter, and then 

 exposed to the air until nearly dry. The pigment, after being 

 reduced to a pulp-like state, is added to an ordinary aqueous solution 

 of gelatin ; and the mass is then filtered warm through linen. If the 

 injection-mass is to be blue, then the gelatin may be dissolved directly 

 in liquid Prussian blue, and the mass filtered through paper. 



As a rule, annelids must be killed before they can be injected. 

 Chloroform and alcohol are the means commonly employed in killing 



* Amer. Natural., xx. (1886) pp. 313-4. 

 t Quart. Journ. Micr. Sci., xx. (1880) p. 306. 



X MT. Zool. Slat. Neapel, vi. (1885) pp. 298-300. Cf. Araer. Natural., xx. 

 (1886) p. 314. 



