CHAPTER XXXVL 537 



from an old culture and securely covered. In from two to three weeks 

 the cultures may be going strongly. It is best to make half a dozen 

 different cultures, placing them at different distances from an oven or 

 thermostat. Not all of them " take." Small flagellates always seem 

 to accompany successful cultures, but the appearance of rotifers and 

 small annelids usually heralds the end of the amoebae. 



Sr. Monica, in a paper in press (Journ. Roy. Mic. Soc. 1921), makes 

 a further contribution to this subject : there are periods of depression 

 in the cultures, new cultures may not " take " immediately, the cultures 

 are best kept in the light near a window, and to avoid extinction of a 

 strain by means of rotifers or small worms, one can only subculture. 



1014. The Growth of Paramcecium in Sterile Culture Medium (by 



R. A. PETERS, Phys. Proceed., 1920). Culture of a race of paramoecia 

 about 50 JJL in length, isolated from a single individual, have been 

 obtained upon the following medium, the cultures being considered 

 sterile for the reasons given below. 



Sodium chloride . . . .0-06 per cent. 

 Potassium chloride .... 0-0014 

 Calcium chloride . . . .0-0012 

 Basic sodium phosphate (Na2HP0 4 ) . 0-0001 

 Acid potassium phosphate (KH 2 P0 4 ) . 0-0001 

 Magnesium sulphate . . . .0-001 



Sodium bicarbonate ... . . 0-002 



Glucose 0-03 



Histidine . . . . . . 0-01 



Arginin 0-01 



Leucin ...... 0-01 



Ammonium lactate .... 0-003 



Ferric chloride Trace 



Potassium iodide .... Trace 



Manganous chloride .... Trace 



The substances are made up with glass distilled water. The con- 

 stituents are autoclaved separately, and the final mixture sterilised 

 by Keating to 80 C. on three successive days. 



The organisms were cultivated first in sterile media in depression 

 slides, experiment showing the most suitable concentration for 

 division. The first divisions were apt to be slow. After a number 

 of individuals have been obtained in this way, they are sub-cultured 

 in test tubes, using all sterile precautions, and when a satisfactory 

 test tube culture has been obtained, it can be used for culture pur- 

 poses as required. A culture has now been kept going by weekly 

 sub-culture upon this medium for three months. (Temperature from 

 15 to 20 C.) 



From successful cultures grown in this way with the paramrecium 

 in question, it was impossible to obtain any bacterial growth (or other 



