GUTTING AND \/>>r.\/i\ TIONB 



too much, and then after, say, twelve hours transferred t<> 

 strong, 90 per cent, and in some cases absolute, alcohol. 

 Alter being transferred to 90 percent alcohol, the specimens 

 should I"' again placed in fresh alcohol, in roomy vials not 



t ilosely crowded, and should resl on a mass of cotton 



so as in»t to lie directly on the bottom of the bottle. 



Fixation of the Histological Elements.— Two thing 

 Lee, are implied by the word " fixing;" first, the rapid kill- 

 ing of the element, so thai it may not have time to change 

 the form it had during life, but is fixed in death in the 

 mil' it normally had during life; and second, the hard- 

 ening of it tu such a degree as may enable it to resist with- 

 nut further change "l' form the action of the reagents with 

 which it may subsequently be treated. 



The mosl convenient fixing agents are picro-sulphuric 

 acid (Kleinenberg's <>v Mayer's formula) and corrosive 

 sublimate. After treating the structure with one of t! 

 it should be washed to remove from the tis£ 



traces of the fixing reagent, [f corrosive sublimate, or osmic 

 acid, or a solution into which chromic acid or a chromate 

 enters, has been used for fixing, the washing may be ilmu- 

 with water; but if picric acid has been used, the washing 

 should be done with alcohol. 



Dehydration. As soon as the fixing agent is removed, the 

 water of the tissues must be removed; this is done by plac- 

 ing the object gradually in alcohol, at first in 50 per cent 

 alcohol for two hours, F0 per cent for six to twenty-four 



hours, 80 percent Beveral hours, 95 per cenl tu ■ three 



hours, and absolute alcohol time enough for com] 

 saturation. 



For insects, especially, Mayer's fluid seems preferal 

 He prepares it as follows: distilled water b ., sulphuric 



arid 2 vols., picric arid, as much as will < e; i 



As this fluid Aov* not diffuse very raj illy through thick 

 chitin, Mayer directs that inserts should be opened with 

 sore, and the body-cavity at once filled with the solution 

 by means of a pipette. A large quantity of the solution 



