APPENDIX 193 



F. Methods of Quieting Ciliated Protozoa 



Formalin method. — Add one drop of full-strength formalin 

 to 50 c.c. of water filtered from the culture containing the 

 paramecia. Place in a watch glass a measured amount of 

 water taken from the culture and containing many para- 

 mecia. Pour into this an equal amount of the water to 

 which the drop of formalin was added, making a solution 

 of one drop to 100 c.c. The movements of the paramecia 

 will gradually become slower until the animals die without 

 distortion in about ten minutes. One thus sees the shape 

 and movements very easily. The danger with a large class 

 is that the student will continue the study of a single 

 preparation too long, not realizing that the specimens are 

 assuming an abnormal appearance. The method is excel- 

 lent with a small group under close supervision by the 

 instructor. Hypotrichs may be quieted in a similar manner. 

 Some protozoans, notably Didinium nasutum, remain with 

 cilia and general contour intact for many minutes after 

 death. Trial of various dilutions of the formalin mixture 

 should be made, as the optimum seems to differ slightly for 

 different species and in different cultures. 



Gum tragacanth method. — Solutions of various gelatinous sub- 

 stances may be used for quieting ciliates, the method being 

 to place the animals in a fluid that impedes progress without 

 at first causing distortion. Gelatin, gum arable, and the 

 jelly obtained by soaking quince seeds in water have been 

 used by investigators. The authors have found none of 

 these to be satisfactory for use with students. Recently, 

 we have used tragacanth as follows: Flake tragacanth, ob- 

 tainable at drug stores, is ground in a mortar and then 

 placed in cold water to make a thick jelly. Dilute the stock 

 thus obtained and add to water containing paramecia in a 

 watch glass or on a slide. A few trials will show the vis- 

 cosity most advantageous for impeding movement without 

 immediate injury. 



Vaseline-sealed mounts. —Spread a line of vaseline around an 

 area corresponding to that of the cover glass that is being 

 used and place a drop of the culture within the pen thus 

 formed. Add cover glass so that a sealed chamber will 

 enclose the water containing the paramecia or other pro- 

 tozoa. Practice is necessary to make such preparations 



