8 MICROSCOPICAL RESEARCH 



to twenty-four or more hours, according to the size and density of the 

 pieces dealt with. The specimens should now be soaked in water for 

 four to six hours, if small, and for twenty-four or more hours, if large, 

 to free them as much as possible from the acids, the water being 

 changed at intervals during the process ; or a much better method is 

 to tie up the specimens in a muslin cloth, place them in a dish, and 

 allow a stream of water to pass through them. The specimens should 

 now be graduated through 25 per cent., 40 per cent., 60 per cent, 75 

 per cent, 85 per cent, and 92 per cent alcohol, in which they may 

 remain for future use. The specimens must stand in each strength of 

 alcohol for one or two hours during the first few changes, and for eight 

 to twelve hours during the latter two or three changes to prevent 

 contraction of the tissues. The method of "graduating" applies in 

 every case when it is necessary to transfer delicate specimens (or 

 sections) from a dense to a light medium, or vice versa. 



2. Chromo-acetic Acid Solution. 



I gram chromic acid, 

 I cc. glacial acetic acid, 

 98 cc. water. 



Stock solution. 



This solution is much cheaper than Flemming's fluid, and may be 

 kept ready for use in quantities suitable for one's requirements. It is 

 the best all-round fixative for general purposes. The solution is a 

 strong one, and should be weakened by the addition of water when it 

 is desired to fix very delicate objects, or weaker solutions may be made 

 up to suit individual requirements. In my own work it is used in its 

 full strength for large pieces of tissue, developing vegetative buds, or 

 male and female cones of pinus, vegetative buds and fertile spikes of 



