x PREFACE TO THIRD EDITION 



on the effect of temperature upon the viability of 

 bacteria in water are included in Chapter I. The recent 

 recommendations of the Committee on Standard 

 Methods are discussed in Chapters II and IV; in 

 particular, Chapter IV, dealing with the 37 count, 

 has been expanded. We cannot bring ourselves to 

 agree with the recommendation of the committee that 

 the 37 count should replace the 20 count; but we are 

 entirely in accord with the resolution adopted by the 

 Laboratory Section of the American Public Health 

 Association at its Washington meeting that both 

 determinations should be made in ordinary routine 

 water examinations. Indeed, this is the position we 

 have maintained in both our earlier editions. 



Chapter V, dealing with the isolation of specific 

 pathogenes from water, has been extensively rewritten 

 and extended. The use of the Jackson bile medium 

 for the preliminary enrichment of the typhoid bacillus 

 has become general since 1908 and a number of suc- 

 cessful isolations have been reported by its use; so that 

 this procedure promises to be of increasing importance 

 in the future. 



In regard to the isolation and identification of 

 bacilli of the colon group we feel that the time has come 

 for a change from the usual American practice of the 

 past. The five standard tests for " typical B. coli " 

 established by the Committee on Standard Methods 

 in its 1905 report have come to seem more and more 

 illogical and unscientific to most practical water bac- 

 teriologists. The conviction has grown that they go 

 either too far or not far enough. For waters, in the 



