30 FIXING AGENTS. 



be mentioned here. Although quite superseded for general work by other 

 reagents, it may possibly still be found useful for certain special purposes. 

 For instance, for the preservation of Medusce the following process has been 

 recommended (by Pagenstecher). Take two parts of common salt and one 

 of alum, and make a strong solution. Throw the animals into it alive, and 

 leave them there for twenty-four to forty-eight hours. Preserve in weak 

 alcohol. A saturated solution of alum in sea-water preserves very well the 

 forms of Salpidce, Medusce, Ctenophora, and other pelagic animals. It 

 constitutes a preservative medium in which the objects may remain till 

 wanted. 



According to my experience, it is not to be recommended for any but the 

 very coarsest work. It should be noted, however, that Ranvier, Traite Tech- 

 nique, p. 279) found that it fixed cartilage-cells better than any other reagent. 

 He employed a solution of 0'5 per cent. 



44 c. Permanganate of Potash (DuP^8si8,Bull.Soc. Vaud.8ci.Nat., 

 2, ser. xv, pp. 278280, 1878).- A strong solution in water. I find this 

 reagent has very slight penetrating power, and, besides, macerates some 

 tissues. It is therefore not adapted for general use, but it preserves very 

 well the forms of cells, and has one great virtue, it kills, I fancy, more 

 rapidly than any other agent I have been able to find ; even 2 per cent, osmic 

 acid is not equal to it in this respect. I have found it sometimes very 

 valuable for the study of isolated and very contractile cells, such as some 

 spermatozoa. 



