14 ILLINOIS BIOLOGICAL MONOGRAPHS [134 



Specimens transferred from xylene to a solution of parafi&n in xylene or 

 from a saturated solution of paraffin in xylene to melted paraffin are 

 usually injured by the appearance of gas bubbles in the tissues and conse- 

 quent tearing and distortion. To avoid this the following method of infil- 

 tration was introduced. Pieces of solid paraffin are successively added to 

 the xylene containing the specimens until the solution becomes saturated. 

 When the solution is saturated at room temperature the dish is placed in 

 a warming oven or on the top of the paraffin bath and the process con- 

 tinued till saturation is again reached. The infiltration to this point usually 

 requires two to three days. The dish is now placed in the paraffin bath 

 and the process continued rather rapidly until the solution becomes practi- 

 cally pure paraffin. The specimens are then transferred to pure paraffin 

 and imbedded after about two hours. The entire period during which the 

 specimens are left in the paraffin bath is usually not more than four hours. 



For imbedding Gruebler's best paraffin with a melting point of 56 to 

 58° C. was found to give the best results. The ordinary paraffins were 

 found to be either too soft or too brittle for this work. Parowax, the 

 Standard Oil product on sale at nearly all groceries, would be an excellent 

 medium if the temperature of the sectioning room could be kept down to 

 about 15° C. 



For sectioning specimens imbedded in the hard paraffin at ordinary 

 room temperature it was necessary to dip the trimmed block into melted 

 soft paraffin. After cooling the soft paraffin was removed from all sides 

 except the lower. Blocks treated in that way, when sectioned 7 to lO/z thick, 

 produce beautiful ribbons in which the sections show no evident shrinkage 

 or rolling. 



All cross sections and most of the longitudinal sections were cut 7/x thick. 

 Longitudinal sections of specimens in which the adult cuticula had been 

 formed had to be cut 10)U and even then gave only poor results on account of 

 the unequal expansion and contraction of different parts when the sections 

 were cut. Cross sections of such specimens also showed distortions from 

 the same causes. In younger specimens in which the cuticula was still soft 

 the sections could be flattened out fairly well by placing them on water on 

 a slide and warming the slide suddenly to the point where the paraffin 

 began to become clear but did not become completely melted. Even with 

 that treatment the cuticula often retained a wavy outline not normal to 

 the living specimen. For later stages the warming usually had to be con- 

 tinued until the paraffin was completely melted. Good results were 

 obtained with such specimens when the slide was placed in the paraffin 

 bath for half an hour or more until the water had evaporated from under 

 the ribbons. For that purpose the bath must be warm enough to melt 

 the paraffin as otherwise blistering takes place and the sections may be 

 ruined. 



