AXIS-CYLINDERS 497 



throughout a great distance from those elements which have 

 remained uncoloured. 



Axis-cyhnders are generally impregnated only as long as they 

 are non-mcdullatcd. In the adult the method stains nerve-cells 

 and their processes so far as these are not myelinated ; but if it 

 be wished to impregnate throughout a great length the axis- 

 cylinders, their arborisations and collaterals, the method is best 

 applied to embryos or new-born animals, at a time when nerve- 

 fibres have not yet become surrounded by their myelin sheath. 



Nervous tissue is not the only thing that is impregnated in 

 these preparations : neuroglia, connective tissue, fibrils, etc., 

 also become stained, and the method has been applied with 

 success to the study of bile capillaries, gland ducts, and the like. 

 Both on account of this peculiarity and of the fact that the 

 impregnation may be limited sometimes to certain elements, 

 sometimes to others, care should be exercised in the interpretation 

 of the results obtained. A further source of possible error is 

 found in the formation of precipitates which may, up to a point, 

 simulate dendrites and other structures. 



The Golgi methods have been applied with success, also, to 

 tissues of invertebrates — insects, Lwnhricus, Tubifex, Helix, 

 Limax, Eistomum, Astacus, Actinida, etc. 



The methods have been described at length by Golgi in Riv. Sperim. 

 Freniatr. T, 1875 ; Arch. p. le Sc. Med., iii, 1878 ; Arch. Ital. Biol., vii, 

 1886, pp. 15 et seq. ; Opera Omnia, Milano, I and II, 1903, and many 

 other pubhcations. A valuable account of the rapid process has been 

 given by v. Lenhossek in his Feinere Ban d. Nervensy stems, 2nd ed., 

 1895, and of both Golgi's methods and their modifications by Kallius 

 in the art. " Golgische Methode,'" in the Enzyk. d. mik. Technik I, 1910. 



1027. Golgi's Bichromate and Nitrate of Silver Method. Slow 

 Process, (a) The Hardening. The tissues must be hardened 

 in a bichromate solution. Either pure potassium bichromate 

 may be employed or Miiller's fluid. (The reaction can be obtained 

 with Erlicki's fluid, but this is not to be recommended.) The 

 normal practice is to use potassium bichromate, beginning with a 

 strength of 2 per cent, and changing this frequently for fresh 

 solutions of gradually increasing strength — 2\, 3, 4, and 5 per 

 cent. The tissue should be as fresh as possible, though satis- 

 factory results may sometimes be obtained from human material 

 collected at the P.M. table even twenty-four to forty-eight hours 

 after death. It should he divided into pieces of not more than 1 cm. 

 or \\ cm. in size. 



The most difficult point of the method consists in finding out 

 the exact degree of hardening, after which the material can be 

 successfully submitted to the further treatment. In summer 

 good results may be obtained after fifteen to twenty days of 

 hardening, and the material may continue to be in a state suit- 



