DESICCATION IN PHILODINA ROSEOLA. 349 



sharpness. By proper manipulation of the light through the 

 condenser the unstained specimen becomes practically as favor- 

 able for examination as that stained in neutral red. 



In preparing dried animals for sectioning large numbers of 

 active animals, free from sand, were put in Syracuse watch 

 glasses and the latter placed in an oven at about 40 degrees 

 Centigrade. While the desiccation process is always fatal to a 

 few animals in each lot which is being dried, I can affirm what 

 Jacobs has already pointed out, namely, that in the case of 

 animals dried on clean glass the mortality is lowest when the 

 temperature is about 40 degrees Centigrade and the moisture is 

 not allowed to pass off too rapidly. 



In preparing undried rotifers for sectioning a large number 

 was collected in a test tube and anesthetized with the cocaine- 

 methyl-alcohol mixture of Rousellet. When the animals were 

 completely relaxed the excess liquid was drawn off and the fixing 

 fluid poured upon the entire mass. After fixation the material 

 was washed thoroughly, passed rapidly through the alcohols, 

 cleared in xylol and embedded in paraffine of 54-56 degrees 

 melting point. Sections were cut 3-5 p. in thickness. 



In the case of the dried animals the fixative was poured directly 

 upon them and allowed to act from twenty to thirty minutes. 



Several fixing fluids were employed. Bouin's picro-acetic 

 formol was not very satisfactory. A solution of saturated cor- 

 rosive sublimate with 5 per cent, acetic acid was used hot. This 

 was quite satisfactory in that its action was almost instantaneous 

 and the preservation of structures faithful in most respects. 

 Beauchamp ('09) says that sublimate fixation was very poor in 

 the forms he studied. He does not state the exact formula 

 employed in his experiments but it would appear that he did not 

 try the one mentioned above. By far the best formula for fixa- 

 tion is the osmic-sublimate-bichromate mixture recommended by 

 Beauchamp. 



In staining the sections iron-alum heematoxylin combined with 

 various counter stains gave the best results. The iron-haemato- 

 xylin-eosin-lichtgrim stain of Beauchamp is very valuable. 

 Another combination consisting of safranin, orange G and licht- 

 griin was used with some success. The latter is not so precise 

 as the haematoxylin combination. 



