722 



MEDICAL ENTOMOLOGY 



glycerine before use, to prevent the wax adhering to the glass. When 

 the tissue is ready for embedding, the paraffin wax should be heated in a 

 pot to a temperature slightly above the melting point, and poured into 

 the paper box ; the tissue is then transferred with a pipette or with for- 

 ceps, and arranged as desired for section cutting. If the wax begins to set 

 before the correct arrangement is obtained it may be melted again by a 

 wide bore pipette, heated in the flame. As soon as the tissue is in posi- 

 tion the paper box should be placed in a large vessel of cool water. 

 Always use an excess of paraffin. 



When working in hot climates tissues should not be cut out of the 

 moulds until they are required for section cutting, as the continuous high 

 temperature melts the wax sufficiently to round off the straight edges 

 which are so essential for obtaining good ribbons. The name of the 

 preparation, date, etc., are written on the outside of the paper. 



TEXT FIGURE 3. 



As in all fine histological work, the more quickly the embedding pro- 

 cess is carried out the more satisfactory are the results. The periods 

 used in ordinary pathological work are far too long for small pieces of 

 delicate insect tissue. Everything depends upon the size and density of 

 the tissues, and no rules can be laid down ; the periods which have been 

 found satisfactory for the mid-gut of the mosquito may be taken as an 

 example : Fixation in Bless' fluid, five minutes ; seventy per cent alcohol, 

 five minutes, with two changes, to wash out the acid ; eighty per cent, 

 ninety per cent, and absolute alcohol, five minutes each, with two 

 changes of the last, the first containing a minute trace of watery eosin 

 solution ; xylol, three minutes, or till cleared ; paraffin, of as low a melting 

 point as the climate permits, five minutes. 



In view of the short period of immersion and the small size of most 

 entomological specimens the paraffin bath is not so convenient to use as 



the copper plate method devised by Stephens and 

 Use of the copper ~, . , A11 , , , r 



plate Christophers. All that is required is a slab of copper 



three inches broad and about a foot long, mounted 

 on a tripod and heated at one end by a spirit lamp. A series of 



