On the Growth of certain Fresh-water and Soil Protista. 155 



difference in osmotic pressure or to the influence of some constituent, organic 

 or inorganic, in the tap water. 



An attempt was made to discover which of these was the determining 

 influence. An artificial tap water was made up from an analysis of Thames 

 water furnished us by Mr. W. W. Fisher. This contained : — 



Parts per 100,000. 



NaCl 2-8 



NaN0 3 0-7 



MgS0 4 1-4 



CaS0 4 2-8 



CaC0 3 22-3 



Si0 2 1-0 



Total solids 31-0 



Somewhat conflicting results were obtained when this artificial Thames 

 water was used to replace natural tap water : on the whole the growth 

 obtained was not so good as when natural tap water was employed, but 

 since it was possible to obtain quite good growths with the artificial medium, 

 it must be concluded that the superiority of the media containing tap 

 water is due to some slight alteration in the proportions of the inorganic 

 constituents. 



Having determined the optimum conditions for growth as far as the 

 inorganic constituents are concerned, namely, 4 c.c. of Miquel solution + 6 c.c. 

 natural tap water, the question of the nature of the organic matter used by 

 the Euglena was then taken up. 



In the experiments given below, the ordinary method of inoculation by 

 means of a capillary pipette was employed, and, in addition, another method 

 which gives more rapid results. In this second method, an old culture tube, 

 in which Euglena has been growing for a long period, is taken. In such a 

 tube there is a ring of encysted Euglena adhering to the glass at the surface 

 of the liquid. The liquid is poured away and the encysted Euglena, which 

 is very firmly attached, may then be thoroughly washed with tap and distilled 

 water. In this way a practically pure culture of Euglena may be obtained 

 on adding the appropriate culture medium, though in no case has it been 

 found possible to obtain a sterile culture free from bacterial contamination. 



The following chemically pure substances were added to the " optimal 

 Miquel " mixture and the tubes inoculated with Euglena, with the results 

 subjoined. 



VOL. LXXXVIII. — B. N 



