48 CASPER 0. MILLER. 



some forms essential^ to furnish them a mechanical support 

 as a means of getting out of the water. 



The medium which has proven the most generally useful is 

 prepared as follows. A handful of hay is placed in a jar and 

 washed repeatedly until the water remains colourless. It is 

 then covered with fresh water and allowed to soak overnight. 

 The following day the water is poured off, filtered, diluted with 

 fresh water until it is of a white-wine colour, and 2 per cent, 

 of milk is added to the infusion. It is then filtered, put into 

 a flask, and sterilised for future use. The macerated hay is cut 

 and placed in Erlenmeyer flasks ; the first portion is cut short 

 enough so as to form a tolerably compact layer in the bottom 

 of the flask to the depth of 1 cm.; the rest is cut sufficiently 

 long to form a very loose layer reaching about two thirds the 

 way up the sides of the flask, care being taken not to allow any 

 of the stems to reach the cotton. Sufficient water is placed in 

 the flasks to cover the hay, and they are sterilised for fifteen 

 minutes. On the following day fresh water is substituted, and 

 they are again sterilised. The water is once more poured ofi", 

 and enough of the hay infusion and milk previously prepared 

 is added until it is about 1 cm. deep. The flasks are then 

 sterilised in a steam steriliser for ten minutes on three suc- 

 cessive days. They are then ready for use. 



After soaking the hay for twenty-four hours in water, and 

 boiling it several times in fresh water, about all of the soluble 

 substance has been extracted, and the diluted hay infusion 

 with 2 per cent, of milk is added; we thus have a medium of 

 tolerably uniform composition. 



Of the cultures gotten from the air several contained mould 

 fungi, which were eliminated by putting the cultures in the 

 oven at a temperature of 37° C. 



One culture contained chroococci, and these were eliminated 

 by keeping a series of cultures in a dark closet. It is not 

 possible in every case to eliminate other protozoic forms that 

 may be present, but one may at times succeed by taking ad- 

 vantage of the fact that the encysted forms withstand drying. 

 In this way one may sometimes succeed in separating Myce- 



