METALLIC STAINS (IMPREGNATION METHODS). 245 



a normal structure of the tissue. It is thus that very often 

 impurities in the specimen have been described as stomata of 

 the tissue. 



If the solution be taken too weak for instance, I : 500 or 

 1 : 1000, or if the light be not brilliant a general instead of 

 an interstitial stain will result ; nuclei will be most stained, 

 then protoplasm, and the intercellular substance will contain 

 but very little silver. 



The tissues should be constantly agitated in the silver- 

 bath in order to avoid the formation on their surfaces of 

 deposits of chlorides and albuminates of silver, which would 

 give rise to deceptive appearances. 



In general in a good "impregnation" the contents of 

 cells, and especially nuclei, are quite invisible. 



Impregnation with silver may be followed by treatment 

 with pic ro- carmine (or other carmine stain), which will bring 

 out the nuclei, provided the impregnation has not been 

 overdone. 



It should be noticed that these impregnations only succeed 

 with f resit tissues, and cannot be made to succeed with 

 tissues preserved in any way. 



339. Silver Nitrate: the Solutions to be employed (RANVIER). 

 The solutions generally employed by RANVIKR vary in 

 strength from 1 : 300 to 1 : 500. Thus 1 : 300 is used for the 

 epiploon, pulmonary endothelium, cartilage, tendon : whilst 

 a strength of 1 : 500 is employed for the study of the phrenic 

 centre, and for that of the epithelium of the intestine. For 

 the impregnation of the endothelium of blood-vessels (by in- 

 jection) solutions of 1 : 500 to 1 : 800 are taken. 



M. DUVAL (Pn'cis, p. 229) recommends solutions of 1, '2, 

 or at most 3 per cent. 



v. RECKLINGHAUSEN used, for the cornea, a strength of 

 from 1 : 400 to 1 : 500 (Die Lympligefiisse, etc., Berlin, 1862, 

 p. 5). 



ROBINSKL (Arcli. <li' Plnjsiol., 1869, p. 451) used solutions 

 varying between O'l and 0'2 per cent., which he allowed to 

 act for thirty seconds. 



REICH (Sitzb. d, wien. Akad., 1873, Abth. 3, April; Zeit. 

 f. iviss- Mile., i, p. 397) takes solutions of from 1 : 600 to 



