422 CHAPTER XXXII. 



757. SEHRWALD'S Gelatin Process (Zeit. f. iviss. Mik., vi, 4, 

 1889, p. 456). 



GOLGI'S process frequently gives rise to the formation at the 

 surface of the preparations of voluminous precipitates that 

 are destructive of the clearness of the images. SEHRWALD 

 finds that this evil can be avoided by putting the tissues 

 into gelatin solution before bringing them into the silver- 

 bath. A 10 per cent, solution of gelatin in water may be 

 made. The tissues are imbedded in this, in a paper im- 

 bedding box, with the aid of a little heat (the gelatin melting 

 at a sufficiently low temperature), and are brought therein 

 into the silver-bath. After the silvering the gelatin is 

 removed by warm water saturated with chromate of silver. 

 MARTINOTTI wraps the tissues simply in blotting-paper, but 

 this does not appear to be efficacious. 



Modifications concerning the Preservation of the Preparations. 



758. Cutting and Mounting. Many most elaborate methods 

 have been proposed with the object of fixing the stain so 

 that the preparations may bear imbedding in paraffin and 

 the sections bear mounting under a cover. None of them 

 have met with much favour. 



SALA (Zeit. f. wiss. Zool., lii, 1, 1891, p. 18; Zeit. f. wiss. 

 Mik., viii, 3, p. 389), in a paper written in Golgi's labora- 

 tory, finds Greppin's hydrobromic acid variation ( 759) not 

 merely useless, but hurtful. And he thinks that SEHRWALD' s 

 process (infra) for imbedding .the material in paraffin with 

 the object of getting very thin sections is a mistake. The 

 chief quality of GOLGI'S process is that it admits of the 

 following of nerve-cell processes for a very great distance. 

 Evidently this cannot be done with very thin sections. It 

 is better simply to wash the preparations taken from the 

 silver-bath with water, fix them to a cork with gum, put 

 the whole into alcohol for a few hours to harden the gum, 

 and cut with a microtome without imbedding. 



An elaborate discussion (for which see previous editions) 

 between SEHRWALD (Zeit. f. wiss. Mik., vi, 1890, p. 443), 

 SAMASSA (ibid., vii, 1890, p. 26), and FICK (ibid., viii, 1891, 

 p. 168) furnishes the net practical result that watery fluids 



