462 AXIS-CYLINDER AND DENDRITE STAINS. 



and put for a second time into the silver bath, where they should 

 remain from thirty-six to forty-eight hours. It is important to find 

 out the proper duration of the first hardening. If it has been too 

 long (four days) or too short (one day) the second impregnation 

 will not succeed. In this case a third impregnation may be resorted 

 to, the objects being again treated with the weak osmium-bichromate 

 mixture and then again with the silver nitrate solution. I find that 

 this modification, which is the most important that has hitherto 

 been made, gives excellent results if one proceeds by tests, viz., 

 re-transferring into the weak osmium-bichromate mixture those 

 pieces in which the reaction has been found to have succeeded 

 to some extent. 



887. KOLOSSOW'S Modification (see ZUSCHTSCHENCO, Arch. Mikr. Anat., 

 xlix, 1897). Tissues are hardened for one to seven days in 3 to 5 per 

 cent, potassium bichromate containing 0-25 per cent, of osmic acid. They 

 are then washed quickly in distilled water, dried with filter paper and 

 transferred for two to three days into a bath of 2 to 3 per cent, silver 

 nitrate to which 0-25 to 0-5 per cent, of osmic acid has been added. 

 This is a good modification for sympathetic ganglia. 



888. GOLGI'S Processes for the Rejuvenation of Over-hardened 

 Tissues. Tissues which have been too long in the osmium-bichro- 

 mate mixture will no longer take on the silver impregnation. They 

 can, however, be made to impregnate by one or the other of Golgi's 

 so-called processes of rejuvenation. These can be carried out in 

 various ways given here with sufficient detail, as they may be of 

 great use not only for rejuvenating ordinary pieces of central nervous 

 system, but also, and particularly, for the staining of nerve-endings 

 in glandular and other tissues, internal apparatus, spiral filaments 

 of peripheral nerve-fibres, etc. 



Golgi at first suggested washing the over-hardened pieces in a 

 half-saturated solution of copper acetate until they no longer give 

 a precipitate, afterwards putting them back again for five or six 

 days into the osmium-bichromate mixture, and subsequently 

 transferring them into the silver nitrate solution. 



Later he advised leaving tissues in 3 to 4 per cent, copper sulphate 

 or 1 to 2 per cent, arsenic acid. After one, two and three days some 

 pieces are brought back into the osmium-bichromate mixture in 

 which they had been hardened, or into a weaker one, proceeding 

 further as in the rapid process, viz., as if the pieces had been 

 freshly fixed in the osmium-bichromate mixture. 



More recently Golgi appears to have preferred mixtures of equal 

 parts of 2 or 3 or 4 per cent, copper sulphate or acetate and 4 to 5 per 



