DENDRITES 501 



spinal ganglia, or for two to six days for the cord itself. The encephalon 

 of these subjects may be treated in just the same way, without being 

 dissected out. 



V. Lenhossek (op. cit.) recommends for human foetal cord two to three 

 days for neuroglia, three to five for nerve-cells, and five to seven for 

 nerve-fibres and collaterals. 



Cerebellum of new-born subjects three to five days in the hardening 

 mixture. 



Cerebral cortex of young subjects two to three days (mice), or as long 

 as five (rabbit, cat) ; cortex of adults, eight to fifteen days. The most 

 favourable region of the brain is the Ammon's horn, especially in the 

 rabbit. 



Retina — twenty-four to forty-eight hours in the mixture, then 

 " double " impregnation (§ 1033). 



Sympathetic. Sala, L. (Mon. Zool. Ital., iii, 1892) found the inferior 

 cervical ganglion particularly suitable for staining by Golgi's rapid pro- 

 cess. He proceeds thus : osmium bichromate mixture, three days ; 

 quick wash in distilled water ; silver bath, two to three days ; further 

 wash in distilled water and passage into the same osmium-bichromate 

 mixture for about four days : a third impregnation can be resorted to, 

 in which case pieces should remain in the hardening fluid for five to 

 seven days. 



Spinal cord of larvce of Amphibia. The entire larvae (best 2 to 2-5 cm, 

 long) should be put for two to five days into the hardening mixture, and 

 for one to two into silver nitrate. 



Epidermis of Lumbricus. Three to six days in the mixture, and two 

 in the silver, or double impregnation if necessary. 



Nervous system of Helix (glia-cells). The above mixture for eight to 

 ten days, then silver of 0-75 to 1 per cent. 



As a general rule, the younger the subject the shorter should be the 

 hardening. If it has been too short, sections will have a brownish-red 

 opaque aspect, with precipitates, and irregular impregnation of cells 

 and fibres. If it has been too long, the ground will be yellow, without 

 precipitates, but with no impregnated elements, or hardly any. 



This process has the advantage of great rapidity, and of sure- 

 ness and delicacy of results, and it is the one that has found most 

 favour with other workers. But for the methodical study of any 

 given part of the nervous system Golgi himself prefers the 

 following : — 



1029. Golgi's Bichromate and Nitrate of Silver Method. Mixed 

 Process. Fresh pieces of tissues are put for periods varying 

 from two to twenty-five or thirty days into the usual bichromate 

 solution (§ 1027), Every two or three or four days some of them 

 are passed into the osmio-bichromate mixture of the rapid process, 

 hardened therein for from three or four to eight or ten days, and 

 finally impregnated with silver nitrate and subsequently treated 

 exactly as by the rapid process. 



The reasons for which Golgi prefers this process are : The 

 certainty of obtaining samples of the reaction in many stages of 

 intensity, if a sufficient number of pieces of tissues have been used 

 for the purpose. The advantage of having at one's disposal a 

 considerable time — some twenty-five days — -during which the 

 tissues are in a suitable state for taking the silver. The possibility 



