212 Phylum Arthropoda 



back-swimmers, on the other hand, destroyed several colonies before the 

 trouble was discovered. 



In conclusion it may be added that no particular attention has been 

 paid to the pH of the water, nor to the contained salts. In some in- 

 stances the water was drawn from the municipal mains which in turn 

 are supplied from numerous mountain streams. At other times pond 

 water was employed. So far as could be detected no differences existed 

 in the growth rate of these two types of cultures. 



Such, in brief, has been my experience in culturing Cladocera, for 

 which credit is due to several investigators in other parts of the country, 

 whose verbal or written statements have been followed in large measure. 



A NEW CULTURE MEDIUM FOR CLADOCERANS* 



IN recent investigations in this laboratory it has been necessary to use 

 numbers of cladocerans. In order to raise these animals in quantities 

 and under controlled conditions various culture media have been re- 

 viewed and tested. Most of the existing media call for manure to supply 

 the organic matter, but as manure is so variable the substitution of 

 materials of more constant composition was tried. Wiebe (1930) has 

 pointed out that soy bean meal is superior to manure for plankton pro- 

 duction in pond fertilization, and more recently the U. S. Bureau of 

 Fisheries has found cotton seed meal quite, if not more, desirable for 

 this purpose. It seemed logical, therefore, to substitute cotton seed meal 

 for manure in cladoceran culture media. This change produced a very 

 satisfactory culture medium, having several advantages over the manure 

 infusions as suggested by Banta (1921). [See p. 208.] 



Pond water was filtered through coarse filter paper and added to a 

 mixture of fine garden soil and cotton seed meal (commercial cotton 

 seed meal, as used in dairy feeds), in the proportions of 1 liter of filtered 

 water to 90 grams of garden soil and 17 grams of cotton seed meal. 

 After a thorough stirring, the mixture was set aside at room temperature 

 in large Erlenmeyer flasks for five days. During this period the mixture 

 fermented and produced considerable gas. At the end of five days the 

 supernatant fluid was decanted and then strained through muslin. 

 Analyses showed that the strained fluid contained an almost pure culture 

 of B. coli. The strained fluid was diluted with filtered pond water before 

 using and re-strained through muslin whenever bacterial masses de- 

 veloped. The pH of the final diluted product was adjusted to 7.2 by the 

 addition of sodium carbonate. 



In strong concentration of this medium bacterial masses formed which 



♦Reprinted, with slight changes, from an article in Science 79:59, 1934, by Walter 

 A. Chipman, Jr., U. S. Bureau oj Fisheries, 



