88S SUMMARY OF CURRENT RESEARCHES RELATING TO 



then be half filled with water and ■ 50 cgr. of calcined magnesia 

 added and left to act for 2 or 3 hours, shaking it now and then. Pure 

 hydrochloric acid is then added in 1 gramme doses every 10 minutes, 

 and when the contents of the phial are colourless the operation is 

 completed. To facilitate the reaction the phial may be plunged in 

 warm or boiling water. The absolute purity of the distilled water 

 to be used for the subsequent washings is an essential condition of 

 success. 



In this process we have first the energetic oxidization of the 

 endochrome by the permanganate, then, by means of the acid, there 

 is a disengagement of oxygen (or combustion), and finally the 

 disengagement of chlorine which bleaches. It is to these successive 

 reactions inside and outside the valves, to which must be attributed 

 the perfect cleansing of their silex. By this treatment the delicate 

 species are not corroded, particularly if, before the action of the acid, 

 enough water is added. 



The surfaces of the valves will be found to have lost all their 

 coleacterine, and the minuter details, strias or dots, clearly shown. The 

 author has tried all the different physical and chemical processes 

 which have hitherto been announced, and he has found none which 

 succeed so completely and so regularly. 



Mr. Kitton writes * that whilst theoretically the method appears 

 to be a good one he fears that it will not prove so effective, when 

 much vegetable or animal matter is present, as the old sulphuric acid 

 and chloride of potash process. 



Mounting Sections in Series. — The use of shellac f for fixing 

 sections on the slide, introduced by Dr. W. Giesbrecht, is a very 

 valuable addition to histological methods, as hundreds of small 

 sections may be arranged in serial order, and all inclosed in balsam 

 under the same cover without danger of disarrangement. The 

 method is further extremely useful in mounting larger sections, 

 particularly those composed of loose parts, or parts liable to swim 

 apart. 



The shellac is prepared and used in the following manner : — One 

 part of bleached shellac J is mixed with ten parts absolute alcohol, 

 and filtered. The slide is first warmed to about 50° C, and then a 

 thin film of the shellac laid on by a glass rod drawn once over its 

 surface. Before using, the slide is again warmed, and the shellac 

 surface washed with oil of cloves for the purpose of softening it.§ 



* Sci.-Gossip, 1882, p. 257. 



t MT. Zoolog. Station Neapel, 1881, p. 184. Cf. 0. O. Whitman in Amer. 

 Natural., xvi. (1882) pp. 783-4. Also this Journal, i. (1881) pp. 953-4. 



t Dr. Mark uses the bleached shellac in the form in which it is prepared for 

 artists as a " fixative " for charcoal pictures. It is perfectly transparent, and a 

 film of it cannot be detected unless the surface is scratched. He attaches a small 

 label to the corner of the slide, which serves for the number of the slide and the 

 order of the sections, and at the same time marks the shellac side (otherwise not 

 distinguishable). 



§ Of. this Journal, i. (1881) p. 953, where the following direction is given : — 

 " Before commencing cutting, brush over the shellac layer very thinly with 

 creosote, and then lay the section upon it with as little paraffin as possible." 



