10 TECHNIC 



It was found to be easier to dissect lice and to prepare thefft 

 for embedding if their gastro-intestinal tracts were nearly 

 empty. The absence of fresh blood from the stomach makes 

 sectioning easier, as fixed fresh blood is very hard and brittle. 

 For these reasons we starved all lice for 24 to 48 hours before 

 dissection. 



Very perfect results may of course be obtained with sections 

 of organs removed from the louse; but it was desirable in our 

 work to have the sections include all of the organs and their 

 supporting structures in situ. The abdominal and thoracic or- 

 gans of the louse can be removed with facility by the method 

 described below, and, after arranging upon blocks of some 

 homogeneous, previously hardened tissue, like liver or brain, 

 may be fixed, embedded, and sectioned with ease. To fix the 

 whole louse, penetration of the fixative must be ensured by 

 cutting off the legs through the coxae as closely as possible to 

 the thorax and by removing portions of the lateral margins on 

 both sides of the abdomen. Both of these operations are best 

 done in a trough of paraffin wax, to which lamp black has been 

 added. A good binocular dissecting microscope is essential. In 

 cutting off the lateral margins, which should be done after re- 

 moval of the legs, extrusion of abdominal contents can usually 

 be prevented if a very sharp knife is used and the body of the 

 louse fitted into a small trench, carved in the wax, in such a 

 manner that the lateral margin is supported by the edge. If 

 the lateral margins are properly removed, enough of the mus- 

 culature of the abdominal wall remains to prevent extrusion of 

 the viscera. 



Zenker's fluid, thoroughly saturated with corrosive subli- 

 mate, was the fixative used, and from six to twelve hours was 

 allowed for fixation. Apparently, the length of time in the 

 fixative did not influence the hardness of the chitinous parts. 

 The process of dehydration is most important in influencing the 

 ease of sectioning and the shorter the stay in alcohol, the less 

 brittle becomes the chitin. As a rule, in less than two hours, the 

 lice were run through graded alcohols into oil of cedarwood and 

 were stored in this substance until embedded. Before em- 



