ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 873 



The two great advantages of Dr. Lang's method are (1) that 

 animals so treated are easily stained, and (2) they are killed so 

 quickly that they are left, in most cases, in a fully extended condi- 

 tion. Hot corrosive sublimate kills leeches so instantaneously that 

 they often remain in the attitude assumed the moment before the fluid 

 is poured over them. The colour, however, is not so well preserved 

 as when killed with alcohol, or even with weak chromic acid. 



It should be remembered that objects lying in a solution of corro- 

 sive sublimate must not be touched with iron or steel instruments ; 

 wood, glass, or platinum may be used. 



II. Staining. — It has gradually become a settled custom in the 

 Zoological Station to mount microscopical preparations in balsam 

 wherever this can be successfully done ; and to avoid, as much as 

 possible, the use of aqueous media, both in mounting and staining. 

 The disadvantages often arising from the use of these media in stain- 

 ing alcoholic preparations include the tearing asunder of fragile 

 tissues caused by the violent osmosis set up on transferring an object 

 from alcohol to an aqueous solution ; swelling, the effects of which 

 cannot always be fully obliterated by again transferring to alcohol ; and 

 maceration, which is liable to result where objects are left for a con- 

 siderable time in the staining liquid (as Beale's carmine). These may 

 all be avoided by using alcoholic solutions. Objects once successfully 

 hardened may be left in such solutions for any required time, and when 

 sufficiently stained, be washed in alcohol of a corresponding strength, 

 and then passed through the higher grades without being exposed 

 to water from first to last. As a rule, alcoholic dyes work quickly, 

 and give far more satisfactory results than can be obtained with other 

 media. They penetrate objects more readily, and thus give a more 

 uniform colouring where objects are immersed in toto. Even chitinous 

 envelopes are seldom able to prevent the action of these fluids. 



It is not, however, to be denied that non-alcoholic dyes may often 

 do excellent work, and, in certain cases, even better than can be other- 

 wise obtained. In the case of the Turbellaria, Dr. Lang has found 

 picro-carmine to be one of the best staining agents, and this has been 

 Mr. Whitman's experience with Dicyemidae. As Dr. Mayer has re- 

 marked, the swelling caused by aqueous staining fluids is not always 

 an evil, but precisely what is required by some objects after particular 

 methods of treatment. 



From experiments recently made, Dr. Mayer has found that dyes 

 containing a high percentage of alcohol, stain more diffusely than 

 those of weaker grades, from which he infers that strong alcohol robs, 

 to a certain extent, the tissues of their selective power, and renders 

 them more or less equally receptive of colouring matter. 



1. Kleinenberg's Hcematoxylin* — 1. To a saturated solution of 

 chloride of calcium f in 70 per cent, alcohol, add a little alum and filter. 



* May be used after all hardening fluids. 



t Chloride of calcium, according to Kleinenberg, has no other use than to 

 strengthen the osmotic action between the hematoxylin solution and the alcohol 

 contained in tbe tissues. As chloride of calcium and alum give a precipitate of 

 gypsum, it would probably be better to use chloride of aluminium. 



