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. it 
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 Mississippiriver ata point a short distance below Grafton, 
Ill. Three weeks later this experiment was repeated in a 
similar manner at the same pointintheriver. 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. 
Approxi- 
Dates of | Dates of ; 
EP eens Collection | Discovery Places of Collection. gic Fgh) 
of Samples.| on Plates. Pavel 
Aug. 30, 1900.} Sept. 3 Sept. 6 {Alton. 12 miles, 
Sept. 20, 1900.| Sept. 23 | Sept. 26 |Chain of Rocks, East Shore.} 25 miles. 
Oct. 15 Oct.18 |Tap, Laboratory. 35 miles, 
Oct. 24 Oct. 27 |Chain of 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. prodigiosus 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), 
