394 ANN BISHOP 



for a few hours prior to fixation. This had the effect of removing 

 all the undigested food which otherwise would have obscured 

 the details of nuclear structure. 



Animals destined to be sectioned were fixed in bulk in 

 a watch-glass with warm Schaudinn's solution or with Bouin's 

 solution. The fixative was washed away and the animals 

 were removed to a narrow tube where they were treated with 

 the different percentages of alcohol. When in 50 per cent, 

 alcohol they were lightly tinged with borax carmine to facilitate 

 their orientation in the paraffin wax. They were cleared 

 with xylol. After they had been cleared they were trans- 

 ferred to a watch-glass containing xylol in which parafl&n 

 wax was gradually dissolved. By means of a warm, fine 

 pipette they were transferred to pure wax, contained in a 

 clean porcelain dish, and left in the embedding oven for 

 about two minutes. The animals, together with some of the 

 wax, were dropped upon a glass slide which previously' had 

 been smeared with egg albumen. They were orientated with 

 a warm needle before the wax solidified. The solidified wax 

 was then shaved into small blocks. 



Staining. — Borax carmine, alum carmine, paracarmine, 

 Delafield's haematoxylin, aqueous iron haematoxylin, and 

 Dobell's alcoholic iron haematoxylin all proved to be useful 

 stains. Aqueous iron haematoxylin gave the best results for 

 sections, but the alcoholic modification of the stain was 

 generally used for whole mounts, since in aqueous solution the 

 animals often became detached from the slide. 



Methyl green in 1 per cent, acetic was used for fixing and 

 staining animals not needed as permanent preparations. 



The method generally used for clearing whole mounts was 

 to soak the dehydrated preparations in clove oil for about 

 twenty minutes and to wash away the oil with xylol before 

 mounting in Canada balsam. Hairs were used to support the 

 coverslips because there is a tendency for the unsupported 

 coverslips to crush so large an animal as Spirostomum. 



Observations on Living Specimens. — For isola- 

 tion of an animal for repeated observations it was found best 



