AND DENDRITES 499 



for three to fifteen minutes, though they may be kept in it even 

 for some days without being spoiled. They are then naounted 

 in thick xylol-damar (rather than in balsam), idthout coverslip. 

 Preparations mounted with coverslips in the usual way always 

 go bad sooner or later, whilst those mounted without a cover 

 keep well for years, especially if they are protected from dust and 

 light. 



Instead of creosote and oil of turpentine, fluid cedar-wood oil 

 is now used in Golgi's laboratory for clearing the sections, which 

 are then mounted, without cover, in thick cedar-wood oil. But 

 care must be taken to leave the sections in fluid cedar-wood oil 

 no longer than one hour or so, as otherwise they become brittle 

 and difficult to mount. To make sure of complete dehydration 

 and that no curling of the sections should take place in the fluid 

 cedar-wood oil, they are quickly passed through liquid absolute 

 guaiacol, the whole procedure being carried out as follows : A 

 small quantity of absolute guaiacol is poured in a watch-glass and 

 some fluid cedar-wood oil in two other small glass dishes. Two 

 or three sections are carried from the absolute alcohol into the 

 guaiacol b)' means of a perforated spatula, which is to be used for 

 all the other passages, and cleaned at every passage. After a 

 few seconds the sections are transferred into the first dish of fluid 

 cedar-wood oil and there left for the time necessary to pass 

 another two or three sections from the absolute alcohol into the 

 guaiacol. The first batch of sections is now transferred into the 

 second dish of cedar-wood oil, the second batch into the first 

 cedar-wood oil and a fresh batch into guaiacol, and so on until all 

 sections are collected in the second dish of cedar-wood oil. 



For mounting the sections are lifted, one by one, by means 

 of the same small spatula, and arranged in the order and number 

 one may wish, either on ordinary slides, or on coverslips if the 

 Golgi hollowed-out wooden slides are preferred for definite pre- 

 servation. The excess of cedar-wood oil carried with the spatula 

 is removed by covering the sections, after having definitely 

 arranged them on the slides, first with a sheath of cigarette paper 

 and then with a folded piece of filter paper, to be held by the 

 left hand while the right is passed over it so as to press down the 

 sections and absorb the oil. The whole manoeuvre may be 

 repeated a second time, and then a drop of thick cedar-wood oil 

 put on each section. On the next day the oil which may have 

 run from the sections is cleaned from the edges of the slides and a 

 fresh drop of the thick cedar-wood oil put on the sections, to be 

 protected from dust and light at least until the oil has become 

 quite dry. 



Preparations mounted in this way last for years unaltered ; 

 in fact, I have some which were made in Golgi's laboratory over 

 fifteen years ago and I find that they have kept without change. 



