666 PROTOZOA 



a medium, the cultures must be kept in long, narrow tubes (Bishop, 

 Quart. Journ. Micr. Sci., 67, 1923, p. 405). Jenkin {Brit. Journ. Exper. 

 Biol., iv, 1927, p. 377) concludes that an increase in alkalinity above 

 />H7-4 makes the body wall more permeable to water, the result being 

 that animals swell up and burst. 



Isolation cultures may be made by the " hanging drop " method and 

 sub-cultures made daily. Woodruff kept Paramecium aurelia living 

 continuously for seventeen years on the same bacterial diet. Actino- 

 bolus radians has been kept through 448 generations in sterile spring 

 water with Halteria grandinella as food. The generations are isolated 

 daily, the cultures being kept in small capsules. Similarly, Spathidium 

 spathula was observed through 218 generations with Colpidium colpoda 

 only as food (Moody, Journ. Morph., xxiii, 1912, p. 349). 



Woodcock uses his observation slide (hanging drop on coverslip 

 supported on glass ring over water contained in hollow slide) (Phil. 

 Trans., 207, 1916, p. 379) for cultivating coprozoic protozoa ; they are 

 thus provided with more air than in an ordinary hanging drop. He 

 uses dilute broth as a culture mediiun. 



There are niunerous other media in which amoebae, flagellates and 

 ciliates will flourish. Such cultures are very often kept in test-tubes 

 plugged with cotton-wool to keep them sterile, as is usual in dealing 

 with bacteria. 



1112. A Synthetic Medium. Some interesting experiments have 

 been done by Peters (J. Phys., Iv, 1921, p. 1) in the direction of 

 simplifying the medium used for cultivation of protozoa, and the 

 following details of methods in use in the Department of Bio- 

 chemistry, Oxford, have been supplied by Professor R. A. Peters 

 (November, 1935). 



The saline solution of the medium which seems most useful for 

 growing protozoa has the following composition : — 



NaCl ....... 0-5 gm. 



KCl 001 „ 



CaCla anhydrous ..... 0-02 „ 



MgsSO, 0-01 „ 



AmCl 0-1 „ 



Glass-distilled OH2 1000 c.c. 



To this is added shortly before sterilising 0-3 grm. {i.e. 0-03 per 

 cent.) sodium glycero-phosphate. This sodium salt, being in the 

 form of stable crystals, is found to be more convenient than the 

 ammonium salt originally used and is equally good so long as 

 ammonium chloride is added to the saline solution, as above. 



The ammonium glycero-phosphate used at first in the medium 

 was in the form of a solution containing approximately 50 per cent, 

 of this organic compound. There was no ammonium chloride, 

 but the sodium chloride was 0-06 per cent. 



Small differences in the percentages of the salts have in general 

 little effect, and one finds, as with Ringer's and Locke's solutions 

 (p. 731), that different workers sometimes vary the formula 

 slightly. 



The salts should be Kahlbaum (K) where possible, or other 



