574 PROTOZOA 



cent, solution is said (Harris, ibid., 1900, p. 404) to be better for 

 Vorticellids, but we have had no success in narcotising Zoo- 

 thamnium with their oral cilia extended. 



Menthol is best used by placing a minute crystal under the 

 coverslip with the protozoa, but maceration follows very speedily 

 on cessation of movement in the few ciliates tested. 



Chloral hydrate may be used in 1 per cent, solution or in solid 

 form, but appears to be little better than menthol for ciliates. 



Chloroform water, coloured with neutral red, has proved in 

 our hands as useful as any narcotic for quieting active ciliates 

 and flagellates on the slide. One drop of chloroform rubbed up 

 with 6 to 10 c.c. of a dilute neutral red solution will make a homo- 

 geneous mixture. The protozoa are best mounted in as little 

 fluid as possible, and a minute drop of the mixture placed to one 

 side of the coverslip with a thin glass rod, and allowed very 

 gradually to diffuse in. When this is done successfully the 

 protozoa will move away, and after some minutes, the ones 

 situated about the middle of the preparation will be moving 

 slowly only and the working of the cilia, contractile vacuoles, etc., 

 will be clear, while the protozoa are very little, if at all, distorted. 

 Amytal is used by Lund {Journ. Morph., Iviii, p. 260). Refer 

 also to § 13 where further information is given. 



1123. Addition of Dyes. Intra-vitam Stains. Strictly speaking, 

 all stains are to some extent toxic and consequently slight excess 

 of an intra-vitam stain will more or less check the movements of 

 active forms. To obtain good results the solutions used for intra- 

 vitam work must be extremely dilute and, moreover, dilution 

 must, of course, be effected so far as possible with the liquid in 

 which the organisms are living. The strengths used generally 

 vary between 0-01 and 0-0001 per cent. The dye employed 

 must be as pure as possible. Those generally used for protozoa 

 are : neutral red, methylen blue, Bismarck brown, toluidin blue. 



For mitochondria of protozoa Faure-Fremiet {Arch. d'Anat. 

 micr., xi, 1910, p. 457) and others use janus green, violet dahlia, 

 crystal violet. Brandt (Biol. Centrbl., i, 1881, p. 202) recom- 

 mended " a dilute solution of haematoxylin " as an intra-vitam 

 stain. Taylor {Univ. Calif. Publ. Zool., xix, 1920, p. 417) used 

 a 0-0001 per cent, solution for organelles and fibres of ciliates. 

 Even a 0-5 per cent, solution in water added to cultures rich in 

 flagellates and ciliates is very little toxic to the protozoa, but the 

 same may be said for many other dyes, e.g. indigo-carmine. 



Trypan blue, another intra-vitam stain, is taken up by many 

 tissues. A solution (1 to 2 per cent, in sea water) is recommended 

 by Dr. Lebour (personal communication) for staining the plates 

 of thecate dinoflagellates. The thcca is stained a clear pale blue 

 and the divisions between the plates show up as dark lines. The 

 dinoflagellates are, however, killed and, owing to their extreme 



