592 EXPERIMENT STATION RECORD. 



able to overgrow B. pyocyaneus, but was overgrown by the rest of the bacteria 

 studied. 



"When grown in pure cultures, with the exception of B. proteus rulyarus, 

 the bacteria gave more constant results under aerobic than anaerobic conditions. 



"B. subtiUs showed a marked ammonifying power throughout the work under 

 aerobic conditions. Under anaerobic conditions it regularly decreased the free 

 ammonia and organic nitrogen content, increasing the nitrites and nitrates, espe- 

 cially the latter. 



"B. coll and B. cloacm had a decided reducing action on both the nitrites and 

 nitrates. Under some conditions, as yet undetermined, they reduced the free 

 ammonia content also. 



"B. proteus ruh/anis had a considerable ammonifying power under anaerobic 

 conditions. This was very slight under aerobic conditions and was more con- 

 stant at room temperature than at 37.5° C. 



"The action of B. pyocyaneus and B. mcscntericus ruber was irregular under 

 both aerobic and anaerobic conditions. 



" The experiments in symbiosis showed that the chemical changes followed 

 very closely those of the predominant bacteria in pure culture. Those exi>eri- 

 ments which did not follow this rule, and in which there was a decided pre- 

 dominance of one mi(ro-organi«^m, showed that the bacteria had become pre- 

 dominant too late in the incubation period to effect a marked chemical change. 



"B. coH and B. cloacce, B. coU and B. proteus t^ulgarus gave more constant 

 results when gi*own syrabiotically than when grown in pure culture. These 

 were the only instances of an apparently true symbiotic growth. 



" The results of the experiments, in which more than two bacteria were grown 

 symbiotically, showed that the incubation period, 24 hours, was too short to 

 allow any one micro-organism or any group of bacteria to establish itself clieml- 

 cally." 



These I'esults are taken to indicate that if a group or species of organisms 

 predominates in sewage the changes in its chemical comiwsition may be pre- 

 dicted, but are not consideretl sufficient to justify an attempt to control the 

 flora of tlie sei)tic tank. 



Resolutions concerning disposal of hiunan excreta at unsewered homes 

 (Pub. Health Rpts. [U. S.]. Sup. 22 (1915), pp. 2).— The resolutions adopttnl 

 by the Thirteenth Annual Conference of State and Territorial Health Authori- 

 ties with the U. S. Public Health Service with reference to the disposal of 

 human excreta in rural districts are given. 



RURAL ECOirOMICS. 



Farm management practice of Chester County. Pa.. ^\^ .T. Spfllman, H. M. 

 Dixon, and G. A. BillixNgs {U. S. Dept. A(ir. But. 3J,1 (1916), pp. 99, pis. 2, figs. 

 10). — The more important of the funadmental principles of farm management 

 brought out clearly in this study of the operations of 643 farms, and confirming 

 similar studies, are summarized as follows: 



" The type of farming followed in any given case must be adapted to local 

 soil, climatic, and labor conditions, and especially to local conditions with 

 reference to markets aud market facilities, as well as to the business conditions 

 existing on the individual farms. 



" When the conditions affecting the agriculture of a region have remained 

 stable for a considerable period local agricultural practice tends to become 

 approximately what it should be for best results, provided the practice which 

 gives the best immediate returns does not unfavorably affect soil fertility. 



