LIFE HISTOEY OF TWO RARE CILIATES 353 



bacteria and the waste products of Colpidium, both of which 

 are detrimental to the well-being of Spathidium. After isolating 

 one individual from each line, the rest were kept as reserve 

 stock. Such Spathidium stock was kept in Syracuse watch- 

 glasses and although many attempts were made to cultivate 

 it in larger dishes, none met with success, the free-swimming 

 forms encysting in large numbers within twenty-four hours. 



All dishes used were carefully washed in hot water and dried. 

 The pipettes were also carefully cleaned, a special one being 

 reserved for the purpose of isolation. 



Both living and prepared material were studied. Several 

 fixing agents were tried. A saturated aqueous solution of 

 corrosive sublimate with 5 per cent acetic acid gave the most 

 satisfactory results; the other fixatives led to shrinkage of the 

 cells. In making the total preparations, a quantity of Spathidia 

 were transferred with a capillary pipette to a watch-glass con- 

 taining a small quantity of the fixing fluid. They were then 

 carried over to 70 per cent alcohol and allowed to settle to the 

 bottom of the watch-glass. From this they were transferred 

 to a slide smeared with egg-albumen, the alcohol coagulating 

 the albumen and firmly attaching the ciliates. The slide was 

 next placed for half-an-hour in a strong aqueous solution of picro- 

 carmine and, after destaining with acid alcohol, was carried up 

 through the alcohols to xylol and mounted in balsam. Heiden- 

 hain's iron haematoxylin and polychromatic methylen blue were 

 also used for staining but the results were unsatisfactory. 



The material destined for sectioning was fixed in sublimate- 

 acetic and carried up to absolute alcohol from which it was 

 transferred to an absolute alcoholic solution of magenta. After 

 fifteen minutes in the stain, it was washed in absolute alcohol. 

 Xylol was added drop by drop to the last alcohol until a quantity 

 equal to the amount of alcohol had been used. The material 

 was then transferred to pure xylol. Considerable diflaculty 

 was experienced in imbedding when the paraffin-oven was used, 

 due to overheating the material. In transferring from the first 

 to the second paraffin, which must necessarily be done under 

 the microscope, it is difficult to keep the paraffin at the melting 



