SECTIONING AND DISSECTION OF LICE 11 



bedding, the lice were placed for from one to several days in a 

 mixture of about equal parts of paraffin wax and oil of cedar- 

 wood kept liquid at the temperature outside on top of the oven. 

 For embedding, five changes of paraffin melting at 53C. were 

 employed, and three to five hours allowed. 



Lice prepared and embedded by these procedures could be 

 cut into serial sections, with a very small percentage of failures, 

 at five to six microns. 



6. DISSECTION FOR SMEAR PREPARATIONS OF LICE 



Our endeavor in making smear preparations was to secure in 

 each preparation teased rather than crushed tissues and to in- 

 clude all parts of the alimentary tract, the Malpighian tubules, 

 reproductive glands, and the reniform and tubular salivary 

 glands. For this purpose the dissection is best done upon a 

 microscope slide clamped to the stage of the dissecting micro- 

 scope. 



A louse can be easily held in position upon a smooth glass 

 surface by exerting slight pressure upon its back with a blunt 

 needle or a pair of fine pointed forceps. 



The first step in the dissection is to incise the thorax trans- 

 versely on both sides, nearly severing it at the level of the first 

 pair of legs, but leaving a narrow isthmus in the median line in 

 order to avoid cutting the esophagus. 



The second step is to place the points of the forceps upon the 

 last abdominal segment; then, with a rolling motion compress 

 the last two segments, push forward the contents and retain 

 pressure upon the second or third segment. Now, the last 

 segment and a half should be cut off and, with the forceps still 

 in position to prevent protrusion of the viscera, the head and 

 anterior end of the thorax with the first pair of legs is torn off 

 by traction with the back of a small knife or a sharpened tri- 

 angular shaped needle; the traction should stop before the 

 esophagus is torn. 



The third step is facilitated by placing a drop of salt solution 

 upon the louse. It consists in alternately wiping forwards with 

 the flat of a flexible knife blade from the point of pressure 



