Sididae and Daphniidae 209 



culture medium in use are practically odorless and may be kept in the 

 laboratory. 



The soil to be used handles better if it is of somewhat sandy nature 

 and of not too fine a texture. The main difficulty with soil of very 

 fine particles is the slowness with which the silt becomes settled and thus 

 leaves the medium transparent — but slightly reddish brown in color. 



The culture medium must be well stirred while being dipped out into 

 the culture containers (which are not covered or stoppered) in order that 

 some of the silt may be in each individual culture. Immediately after 

 straining or within two days thereafter the stock medium is at its best. 

 It is ordinarily nearly spent after 5 to 7 days. It has been found that the 

 numbers of bacteria rapidly decrease after about the third day following 

 straining. Presumably the accumulation of by-products of bacterial 

 growth and decrease in numbers of bacteria both contribute to render the 

 older solution less effective as a culture medium. 



The second formula for making up the manure solution medium pro- 

 duces a much more concentrated stock medium. 



Formula II. Garden soil 2 lb. 



Horse manure 12 oz. 

 Pond water 5 qt. 



The handling of this make-up differs from that of Formula I only in that 

 the dilution of the resulting stock medium in preparation for use as cul- 

 ture medium is much greater, ranging from 1 part of the strained 

 medium with 4 to 10 parts of pond water. The writer prefers to use the 

 first formula. Several workers prefer and have excellent results with the 

 second formula. 



The stable tea has been used and found effective by the writer in open 

 cultures (not covered or stoppered) in quantities from 25 cc. to 10 liters. 

 We have made few attempts at rearing mass-cultures of Cladocera. 

 Manure solution culture medium may readily be used for mass-cultures 

 if every few days it is renewed or strengthened by the addition of small 

 quantities of manure (preferably tied up in cloth bags and submerged). 

 Others have with good results occasionally thrown a dead guinea pig or 

 other small animal into a tank in which an abundance of a culture of 

 Cladocera is on the decline. A more precise method for such situations 

 as large laboratory tanks or outdoor tanks is the use of manure or the 

 employment of Dr. Embody 's soy bean meal [see p. 218] or W. A. 

 Chipman's (1934) cotton seed meal [see p. 212] culture methods. In 

 all of these methods the essential feature is the provision of decaying 

 organic matter upon which the proper bacteria may develop and con- 

 tinue to be present in amply large numbers. 



The beginner with the manure solution medium might best first em- 



