COLLECTING, PRESERVING AND APPLIANCES 35 



is then gently boiled for a minute or two so as to expel 

 the air contained within the trachea. As the fluid cools 

 it is necessarily drawn through the stigmata into the body 

 of the insect, and is thus at once carried to all its tissues. 

 It is left in this fluid for a few hours, and is then placed 

 first in 90 per cent., and finally in absolute alcohol. To 

 imbed it, it is first placed for at least twenty-four hours in 

 oil of turpentine and is then imbedded in the usual manner 

 in paraffin. As the various structures are very loosely con- 

 nected it is very important to choose a specimen of paraf&n 

 with a melting point suitable to the temperature of the 

 air of the place in which one happens to be working, for 

 the least curling of the sections is fatal to the production 

 of really satisfactory sections, so that it is well to try a 

 sample of the paraflin in the microtome before employing 

 it for imbedding. In Europe, a parafdn with a melting 

 point of about 105" is not at all too soft for the ordinary 

 temperature of the laboratory, but in the tropics I have 

 found samples melting from 115° to 125° most generally 

 useful ; the former for the cold and the latter for the hot 

 weather. The specimens should be kept for at least six 

 hours in the bath of melted paraffin, and are then, with due 

 attention to orientation, placed in the microtome, which, it 

 is needless to say, should be one of a type constructed to 

 produce ribbands of serial sections, the ordinary pathological 

 instrument being quite useless for this purpose. 



As the sections are to be stained on the slide, albumen, 

 and not creasote-shellac, must be used for fixation. 



A single drop of Mayer's albumen mixture (equal parts 

 white of egg and glycerin, with 1 per cent, salicylate of 

 soda, well beaten up with an egg whisk and filtered) is 

 added to a watch-glass of water and the slide is prepared 

 by brushing over it a liberal allowance of this very dilute 

 albumen, so that the sections rest on a thin layer of fluid. 

 When as many of the series as the slide will accommodate 

 have been arranged in position, the slide is placed on the 

 warm plate of the imbedding apparatus and warmed just 

 sufficiently to flatten the paraffin and no more. It is then 

 placed aside to dry as far as the presence of the glycerin 



