CHAPTER XXXI V. 457 



four to forty-eight hours ; but tissues may remain in the bath 

 without hurt for days, weeks or months. 



(c) Preservation. As soon as a trial has shown that a sufficiently 

 satisfactory impregnation has been obtained, the pieces are brought 

 into 80 to 90 per cent, alcohol. The alcohol is changed two, three 

 or more times, until it remains transparent, even after specimens 

 have been two or three days in it ; for, in view of good preservation, 

 it is necessary that the excess of silver nitrate should be washed out 

 from them thoroughly. 



Sections are now made (see 892). These are to be washed 

 thoroughly in three or four changes of absolute alcohol and cleared, 

 first in creosote, in which they should remain only a few minutes, 

 then in oil of turpentine, in which they are usually left for three to 

 fifteen minutes, though they may be kept in it even for some days 

 without being spoiled. They are then mounted in thick xylol- 

 damar (rather than in balsam), without coverslip. Preparations 

 mounted with cover-slips 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 by 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 



