TEGUMENTARY ORGANS. 369 



and the sections are then brought into picrate of ammonia, 

 and treated as described in the chapter on " Methylen Blue." 

 GEBERO (ibid., x, 2, 1893, p. 244) has also employed this 

 method. He has also made use of simple osmic acid, 

 and of the gold method of ABNSTEIN, for which see previous 

 editions. 



661. Corpuscles of Meissner and of Krause (Cornea and Con- 

 junctiva Bulbi and Palpebrarum). DOGIEL (Arch.f. mik.Anat., 

 xxxvii, 1891, p. 602, and xliv, i, 1894, p. 15) employs 

 the methylen blue method ; for details see previous editions. 



See also LONGWORTH'S methods, Arch. mik. f. An at., 1875, 

 p. 655. 



662. Cornea. There are three chief methods for the study 

 of the corneal tissue the methylen blue method, the silver 

 method, and the gold method. 



For the methylen blue method see Chap. XVII, particularly 

 330 and 331. 



Negative images of the corneal cells are easily obtained by 

 the dry silver method (KLEIN). The conjunctival epithelium 

 should be removed by brushing from a living cornea, and the 

 corneal surface well rubbed with a piece of lunar caustic. 

 After half an hour the cornea may be detached and examined 

 in distilled water. 



In order to obtain positive images of the fixed cells the 

 simplest plan (RANVIER) is to macerate a cornea that has 

 been prepared as above for two or three days in distilled 

 water. There takes place a secondary impregnation, by 

 which the cells are brought out with admirable precision. 



The same result may be obtained by cauterising the cornea 

 of a living animal as above, but allowing it to remain on the 

 living animal for two or three days before dissecting it out, 

 or by treating a negatively impregnated cornea with weak 

 salt solution or weak solution of hydrochloric acid (His). 



But the best positive images are those furnished by gold 

 chloride. RANVIER prefers his lemon-juice method to all 

 others for this purpose ( 353). It is important that the 

 cornea should not remain too long in the gold solution, or the 

 nerves alone will be well impregnated. 



RAN VIE K also recommends this method as the best for the 

 study of the nerves. 



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