AGGREGATIONS OF HIGHER ANIMALS 93 



in the containing vessel. Living in this water the fish 

 condition it by giving off organic matter and carbon 

 dioxide. They are left in the water for twenty-one 

 hours or so, while a similar amount of the same water 

 stands near by under exactly similar conditions ex- 

 cept for the absence of fish. 



At the end of this time the clean control water is 

 siphoned into a number of clean jars, and a small 

 measured goldfish is placed in each. At the same time 

 the conditioned water is siphoned, either with or 

 without removing particles (that is, of excrement, 

 etc.) that may be present, into similarly clean jars. 

 A set of small measured goldfish, like those used in 

 the control jars, are transferred into the conditioned 

 water. These small "assay" fish have been feeding 

 for about two hours before being transferred; the 

 larger conditioning fish are allowed to feed for a 

 somewhat longer time before being washed carefully 

 to remove food residues and replaced in another lot 

 of water to condition that. 



Meantime the jars, 120 of them, are all washed 

 carefully; and after this is done the experimenter has 

 nothing more to do until the next day, except to put 

 the laboratory in order, keep the temperamental 

 steam distilling apparatus running, test the water 

 chemically in several ways, keep his records in order, 



