138 METALLIC STAINS (IMPREGNATION METHODS). 



In general, in a good " impregnation/' the contents of cells, 

 and especially nuclei, are quite invisible. 



Ranvier notes that when tissues are to be impregnated by 

 immersion they should be constantly agitated in the silver- 

 bath in order to avoid the formation on their surfaces of de- 

 posits of chlorides and albuminates of silver, which would give 

 rise to deceptive appearances. 



Impregnation with silver may be followed by treatment 

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

 out the nuclei, provided the impregnation has not been 

 overdone. 



It should be noticed that impregnations only succeed with 

 fresh tissues, and cannot be made to succeed with tissues 

 preserved in any way. 



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

 The solutions generally employed by Eanvier 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'SOO are taken. 



M. DUVAL (Precis, p. 229) recommends solutions of 1, 2, or 

 at most 3 per cent. 



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

 from 1400 to 1500 (Die Lymphgefdsse, &c., Berlin, 1862, 

 p. 5). 



ROBINSKI (Arch, de PhysioL, 1869, p. 451) used solutions 

 varying between 0*1 and 0*2 per cent., which he allowed to 

 act for thirty seconds. 



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

 Zeit. f. wiss. Mik., i, p. 397) takes solutions of from 1 600 

 to 1 400 for the study of the endothelium of vessels by 

 .injection. 



ROUGET (Arch, de PhysioL, 1873, p. 603) employed solutions 

 as weak as 1 750, or even 1 1000, exposing the tissues to 

 their action several times over, and washing them with water 

 after each bath. 



The HEETWIGS take, for marine animals, a 1 per cent, solu- 

 tion ( Jen. Zeit.f. Naturk., xvi, pp. 313 and 324). 



