On the Growth of certain Fresh-tvater and Soil Protista. 153 



The medium used for growing these organisms has been a mixture of 

 inorganic salts given by Miquel in his paper on the growth of diatoms.* 

 To this medium, which contains all the elements necessary for the growth of 

 a green plant, it has been found necessary to add some organic material in 

 order to obtain an active growth of the organism. The composition of 

 Miquel's fluid is as follows: — 



Solution A. Solution B. 



MgS0 4 10 grs. Sodium phosphate 4 grs. 



NaCl 10 „ Calcium chloride 4 „ 



Sodium sulphate 5 „ Hydrochloric acid 2 c.c. 



Ammonium nitrate ... 1 „ Perchloride of iron, sat. sol. 2 „ 



Potassium nitrate 2 „ Water 80 „ 



Sodium nitrate 2 „ 



Potassium bromide ... 0"2 „ 



Potassium iodide 04 „ 



Water 100 „ 



To make up the fluid, 40 c.c. of solution A and 10 c.c. of solution B are 

 added to 500 c.c. of tap water, and the mixture is filtered. 



It was necessary at first to determine the strength of Miquel's fluid best 

 adapted for growing the Euglena. In a number of preliminary experiments 

 it was found that the best growth could be obtained when 4 c.c. of the 

 above Miquel solution were added to 6 c.c. of tap water, the organic 

 matter being supplied by 1 c.c. of hay infusion. The experiment was 

 performed by inoculating the tubes with a very small amount of the 

 stock culture, introduced by means of a capillary pipette. The tubes 

 were kept in diffuse daylight at room temperature ; attempts to hasten 

 the growth by incubation at 75-80° F, were unsuccessful, the Euglena 

 dying, or at any rate failing to flourish at this temperature. In the 

 absence of any organic infusion, the Euglena either failed to develop 

 or else multiplied very slowly, and the fluid in the tube never became 

 crowded with free-swimming organisms so as to appear opaque and green. 

 The addition of 1 or \ c.c. of hay infusion, on the other hand, caused a thick 

 growth which, after the lapse of 10-14 days, filled the tube with myriads of 

 free-swimming individuals, giving a totally different appearance to the con- 

 dition seen in the tubes to which no organic matter had been added. 



It was found, however, that the efficacy of the hay infusion varied very 

 greatly according to the length of time during which bacterial growth had 

 continued in it. Thus, a fresh hay infusion, after being sterilised, was found 

 * Dr. Miquel, ' Le Diatomiste,' No. 9, June, 1892. 



