ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 295 



somewhat in size, but their structure is preserved, and the larvae are 

 effectually destroyed. The liquid often gets filled with sediment and 

 floating particles, to free it from which it should be poured off, strained 

 through a piece of thin muslin, and returned to the plants. 



Osmic Acid for Microscopical Investigations * — Dr. T. B. Red- 

 ding gives directions for preparing the proper solutions of osmic acid 

 for microscopic use : — Take a glass bottle, with a ground-glass stopper, 

 and cover it thoroughly with black paper, so as to exclude all light, 

 covering the exposed parts of the stopper in the same manner. If 

 you have the ordinary capsule containing -^^ oz., and require a 1 per 

 cent, solution, put 3 oz. of distilled water into the bottle and then 

 drop the capsule into it and shake violently, so as to break the cap- 

 sule, or, if that does not succeed, break with a clean glass rod. In a 

 few hours the acid will have dissolved, and the fluid will be ready for 

 use. For removing from the bottle, use a dropping-tube kept espe- 

 cially for that purpose. 



Dr. Redding also describes the method of using osmic acid for 

 staining purposes. (1) By immersing the object in the fluid ; (2) by 

 exposing it to the vapour of the solution ; and (3) a third method, that 

 of injection, which is a modification of the first. The objects he used 

 were the nerve-fibres, nerve-plates, blood-corpuscles, epithelium, pro- 

 toplasmic and other elements connected with or adjacent to the blood- 

 vessels of the frog, toad, kitten, &c., which were stained by first 

 injecting the vessels, through the aorta, immediately after death, with 

 a very dilute solution of osmic acid in water and glycerine, equal 

 parts. Twenty to thirty drops of the 1 per cent, solution should be 

 used to the ounce of water and glycerine, and the injection followed 

 in two or three hours after with an injection of Beale's blue, or with 

 carmine jelly fluid, reduced to a delicate rose-tint by excess of water 

 and gelatine. The preparations may be further differentiated with 

 other stains. 



The vapour method changes the elements less and admits of fur- 

 ther staining processes more readily than any other method. Log- 

 wood and eosin are the best stains to use after treating with osmic 

 acid. Either will give good results with most tissues. In using 

 carmine, it is best to stain the tissues before exposing to the vapour. 

 Sometimes the vapour will attack the carmine and nearly obliterate it. 



For infusoria, algae, &c., fixed and stained with osmic acid, the 

 following is found to act well, both as a stain and a preservative : 

 Picrocarmine, 1 part ; distilled water, 1 part ; glycerine, 1 part ; 

 apply by allowing a drop to run under the cover-glass on the slide. 

 As a hardening agent, osmic acid is valuable for very delicate struc- 

 tures, such as brain, nerve, and embryonic tissues ; especially for 

 soft tissues which are to be cut into sections. For this purpose the 

 following method is best : — Take of a 1 per cent, solution of osmic 

 acid, 1 part ; a mixture of equal quantities of water and glycerine, 

 2 parts ; of a 1 per cent, solution of chromic acid, 2 parts ; alcohol, 

 J part ; mix. The specimen to be hardened should be small. After 

 remaining in the solution a few days or hours, according to size, 



* Proc. Amer. Soc. Micr., Stli Annual Meeting, 1882, pp. 183-6. 



