4 70 JOHNSON. [Vol. VIII. 



wax. A drop of water containing one or more Stentors is 

 placed in each cell, and the specimens examined in turn with a 

 low power of the compound microscope. 



As to killing reagents, no reliable method has yet been 

 found for fixing, in a state of extension, these highly-contractile 

 Infusoria. Hydrochlorate of hydroxylamine, used in .25 per 

 cent solution, neutralized with sodic carbonate, has been recom- 

 mended by B. Hofer^ as a paralyzing reagent, but I have 

 tried it in vain on vS. c<Bruleus. On the other hand, it seems 

 impossible to find an agent of sufficiently rapid action to fix 

 the animal before it contracts. Fortunately, contracted or 

 semi-contracted specimens answer very well for most purposes. 

 I have used for fixation, absolute alcohol, Flemming's chrom- 

 aceto-osmic mixture, i per cent to .25 per cent osmic acid, 

 Merkel's fluid, saturated aqueous solution of corrosive subli- 

 mate, and picro-acetic. The last two have proved the most 

 satisfactory. The picro-acetic mixture I make up as follows: 

 saturated aqueous sol. picric acid, 6 parts ; glacial acetic acid, 

 I part. It gives excellent results used either hot or cold, and 

 should invariably be washed out with 50 per cent to 70 per 

 cent alcohol. 



In staining, two methods have been followed. First, for 

 immediate study, one may fix and stain with a single reagent, 

 such as an aqueous solution of methyl-green, to which a little 

 acetic acid has been added ; or Schneider's aceto-carmine. 

 This method is invaluable for study of the structure of the 

 meganucleus. Neither are lasting stains. For fixed and 

 hardened material, intended for permanent preparations, I 

 find that almost any of the carmine stains are good, while 

 haematoxylin tinges the cytoplasm too deeply. I have used 

 mainly Czokor's alum cochineal and picro-carmine, for they 

 stain the cytoplasm least. In making preparations for study 

 of the nucleus, decolorizing with acidulated alcohol is impor- 

 tant, and should be carried far enough to extract all stain from 

 the cytoplasm. 



I have found it perfectly feasable to imbed Stentors in 

 paraffinc, and cut serial sections 5/* to lO/w. in thickness. Sec- 



1 Zeits. f. wiss. Mikr., vii, pp. 318-326, 1890. 



