ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 151 



materially altered. They may be preserved by several methods, 

 either by treating for twelve to twenty-four hours with a concentrated 

 solution of picric acid, a dilute solution of chromic acid, by Dr. 

 Klein's method with a 5 per cent, solution of ammonium chromate, 

 by iodine, by silver nitrate, or by osmic acid or gold chloride ; the 

 latter are convenient as being quicker. He has most usually em- 

 ployed picric acid. For staining glycerine, magenta * is the best 

 method, as it stains all parts as strongly as desired. To show the 

 general structure alcoholic carminate of ammonia is the most satis- 

 factory, but it does not stain the barb deeply. Other anilin dyes have 

 not been found to answer so well. 



The use of glycerine as a mounting fluid for preparations stained 

 with any of the anilin dyes is at best troublesome,! and sooner or 

 later, in the author's experience, the staining runs and the preparation 

 is spoiled. Solutions of acetate of potash or chloride of calcium have 

 not been found satisfactory, the forms, even of such resistant objects 

 as bacteria, in some cases becoming materially altered by these re- 

 agents. With Canada balsam, even when dissolved in chloroform or 

 turpentine, the preparations have not been found to fade, as has some- 

 times been said to be the case, and as we should have expected ; nor, 

 if they are sufficiently washed in alcohol and passed through oil of 

 cloves, will they run. The risk, however, of both fading and running 

 may be entirely obviated by using benzine as a solvent for the balsam, 

 or by employing it undiluted and liquefied by warmth. 



Killing Hydroid Zoophytes and Polyzoa with the Tentacles 

 extended- 1 — H, C. Chadwick recommends the polyzoon to be placed 

 in a small beaker or clear glass bottle, and allowed to remain at rest 

 for several hours. Now take a dipping-tube drawn out to a very fine 

 point and charge it with absolute alcohol. Having ascertained by 

 means of a pocket-lens that the polypides are fully extended, allow 

 the alcohol to drop very gently from the point of the tube, which 

 should be held just above the surface of the water. The success of 

 the experiment depends largely upon the care with which the first 

 quantity of alcohol is introduced into the water. After the lapse of 

 an hour, if the polypides are still extended, a further quantity of 

 alcohol is added until the quantity reaches 60 per cent. 



After passing through 76 per cent, alcohol, the specimens may be 

 kept in 90 per cent, of the same until required for mounting. Ex- 

 periments with alcohol upon hydroid zoophytes were not so success- 

 ful, but Kleinenberg's picrosulphuric acid solution § gave excellent 

 results. The use of this reagent is attended with much less difficulty 

 than that of alcohol. If the subject of the experiment is a zoophyte, 



* Magenta cryst. 1 part; glycerine 200 parts; alcohol 150 parts; aq. 

 150 parts ; immerse the preparation in the solution for from two to four minutes, 

 according to the depth of colouring required, and then wash. 



t The method is, add an equal bulk of glycerine to the aqueous solution of the 

 anilin dye used, stain somewhat more deeply than requisite, mount on slide with 

 cover-glass in the staining fluid, which is to be gradually replaced as the water 

 evaporates by plain glycerine. 



t Micv. News, iii. (1883) pp. 333-4. 



§ Cf. this Journal, ii. (1882) p. 867. 



