GOO SUMMARY OF CURRENT RESEARCHES RELATING TO 



test-tubes sboultl be cleansed witb bydrocbloric ncid and tben washed 

 with distilled water. After receiving tbe agar solution, the tubes are 

 closed witb cotton, and tben sterilized in tbe steam apparatus for half 

 an bour daily on three successive days. 



As the preparation of tbe agar mass is somewhat complicated, much 

 time and trouble may be saved by turning this work over to some 

 apothecary. 



Tbe best medium of fixation for the elements of blood is a 2 per cent. 

 solution of osmic acid. If a drop of blood from the frog be examined in 

 this medium under the Microscope, it will be seen that both the red and 

 tbe white corpuscles are perfectly preserved in form and structure. The 

 red corpuscles become a little paler than in tbe living condition, and are 

 slightly browned. Tbe corpnschs of mammalian blood are isolated and 

 seen to greater advantage than in any other medium of fixation. As it 

 is important that the acid should be perfectly clear and free from all 

 impurities, it is well to filter before using. 



Method of Procedure. — (1) By the aid of a clean pipette, take a little 

 blood from the heart of a frog, and allow two drops to fall into five ccm. 

 of osmic acid (2 per cent.). Shake a little — tlie sooner the better — in 

 order to separate the elements and scatter them through the whole body 

 of the acid. After standing a while, the blood-corpuscles will be found 

 at the bottom of the tube, tbe deeper layer being formed mainly of red 

 corpuscles, which sink first by virtue of their greater specific gravity. 

 Exposure, 1-24 hours. 



(2) Tbe process of fixation completed, four to five drops of the mixture 

 of blood and osmic acid are allowed to fall from a pipette into the 

 melted agar, which is kept fluid at a temperature of 35^-37° C. By 

 rotating the test-tube the blood-corpuscles are distributed through the 

 agar, and then the whole is poured into a paper box, as in the ordinary 

 paraffin method of imbedding. Within a few minutes the mass stiffens 

 and may be removed from the box to 85 per cent, alcohol for hardening. 

 In thi'ee to six days the mass is hard enough for sectioning, and may be 

 inclosed in elder-pith and cut with the microtome. 



If finer sections are required than can be obtained in this way, the 

 agar block may be imbedded in paraffin in the following manner ; — The 

 block is to be transferred from the 85 per cent, alcohol to bergamot 

 oil (24: hours), tben direct to soft paraffin kept at a tempera- 

 ture of 45° C. After one to two hours, the imbedding process may 

 be completed in the usual way. As the agar is saturated with paraffin, 

 very fine sections may be obtained ; and these may be freed from paraffin 

 with the usual solvents, and then stained. 



(3) Sections thus prepared may be safely treated with nearly all 

 staining media. Methyl-green, methyl-blue, fuchsin, safranin, &c., give 

 the most reliable results. Tbe agar itself is stained only by the most 

 intense anilin dyes (e. g. gentian-violet), but in such cases it loses its 

 colour quickly in alcohol, or in any other decolorizing fluid. 



(4) Sections may be clarified, prejiaratory to mounting, in balsam or 

 dammar, in clove oil, origanum oil, bergamot oil, creosote, &c. Xylol 

 alone should not be used as it causes the sections to curl. 



Preparation and Staining of the Spinal Cord.* — Prof. L. Eanvier, 

 who has been making observations on the transformation of nerves with 



* Joum. de Microgr., xii. (18S8) pp. 112-4. 



