Kirchner — Bacteriological Examination of River Water. 289 



along these lines will lead to more satisfactory and better 

 methods of examination. 



The ultimate object of an examination concerns itself not 

 only with the detection of sewage, but also with the tracing 

 of sewage, so that the source of contamination may be ascer- 

 tained and the responsibility fixed. For the purpose of tracing 

 contamination to its source, and as a means of showing the 

 transmission of bacteria along water channels, resort may be 

 had to B. prodigiosus which is non-pathogenic and which has 

 cultural characteristics that make it easy of detection. This 

 organism was used in our tests, and the following experiments 

 were made. 



A barrel of a pure broth culture of B. prodigiosus was pre- 

 pared and the contents of the barrel (40 gal. ) was emptied into 

 the Mississippi river at a point a short distance below Grafton, 

 111. Three weeks later this experiment was repeated in a 

 similar manner at the same point in the river. This organism, 

 B. prodigiosus, by tests carefully guarded by control methods, 

 was recovered and identified on four separate occasions, and 

 the data bearing on these experiments may be seen in the 

 following table. 



TABLE XI. 



Dates of 

 Introduction. 



Dates of 

 Collection 

 of Samples. 



Dates of 

 Discovery 

 on Plates. 



Places of Collection. 



Approxi- 

 mate Dis- 

 tance of 

 Travel. 



Ausi. 30, 1900. 

 Sept. 20, 1900. 



Sept. 6 

 Sept. 26 

 Oct. 18 

 Oct. 27 



Alton. 12 miles. 



Chain of Rocks, East Shore. 25 miles. 



Tap, Laboratory. 36 miles. 



ChaiQof Rocks, East Shore. 25 miles. 



Based upon these experiments, and especially as previous to 

 these tests ( although over 3,000 samples of river-water had 

 been examined), B. i^^odigiosus had not been encountered in 

 water taken from the river, we are led to the conclusion that 

 bacteria introduced into the current of the river at a place a 

 short distance below Grafton may find their way into the water- 

 supply of St. Louis. 



In experiments made by Dr. Horrocks (J. San. Inst., 1899), 



