174 CHARLES L. PARMENTER 



wide the body cavity. The folds of the viscera were pulled 

 apart and the whole larva was plunged into the fixative. This 

 secured immediate and uniform fixation. The operation requires 

 less than a minute and the incisions are apparently painless, for 

 the larva does not often struggle. 



2. The body walls, lungs, and viscera were removed from the 

 body of the larvae before fixing, either in the field or at the 

 laboratory. The peritoneum was fixed in situ on the body walls. 

 Only normally inflated lungs were used, and these were ligated 

 anteriorl}" before removal from the body to prevent them from 

 collapsing. After fixing one or two hours, they were cut into 

 two or more flat longitudinal strips and returned to the fixative. 

 The mesentery, attached to the intestine, was spread out flat 

 on a piece of glass and the whole immersed in the fixative with 

 the tissue beneath. 



Fixatives 



The fixatives used were: 1) Flemming's stronger solution, 

 thirty hours; 2) Eouin's solution, forty-three hours; 3) Bouin's 

 solution, to which was added 1| grams of chromic acid crystals 

 per 100 cc, twenty to twenty-four hours; 4) Hermann's solution 

 with two parts of osmic acid (Lee, '13, p. 38) twelve to eighteen 

 hours; 5) a solution of saturated picric acid 75 cc, formalin 15 

 cc, glacial acetic acid 10 cc, urea crystals 2 grams, thirty to 

 forty-three hours. The urea should be added gradually to the 

 solution warmed to about 40°C., otherwise a precipitate is 

 formed. 



It is a difficult matter to decide which solution gave the best 

 fixation. The prettiest cells were fixed in Hermann's and the 

 chromic acid modification of Bouin's fluid. However, the peri- 

 toneum preparations of the osmic fixatives were a little thicker 

 and less transparent than the others. If any fixative should be 

 exclusively chosen, I believe it should be the chromic acid modi- 

 fication of Bouin's solution, because of its excellent fixation, 

 convenience, and economy. 



The peritoneum was removed as follows: The two sides of 

 the body wall were detached by an incision along the back 



