116 
IOWA ACADEMY OF SCIENCES. 
instead of taking the tube with the highest amount of acid 
in which growth occurs (which would probably contain 
only Bacilli coli ), Hankin* takes the one just below for 
the inoculation of a new series. Finally pure cultures are 
isolated on the agar plate and tested by various sub- 
cultures.’’ 
In a bacteriological examination of waters it is essential 
to carry out the rules laid down by the American Public 
Health Association and those adopted by the Massachusetts 
State Board of Health, and the methods used in the lab- 
oratory of the Boston Institute of Technology. The 
methods consist essentially in making quantitative an- 
alyses, and first of all it is important that all media should 
be perfectly sterilized for the least amount of error in this 
respect will make the results of no value. In spite of the 
fact that the greatest care is used in the making of media 
it sometimes, happens that some of the tubes become in- 
fected in some way. As to the use of media, it is generally 
admitted that ge, i tin, agar agar, and litmus lactose agar 
and the fermentation tube with dextrose are important in 
obtaining reliable results. 
Quite recently Dr. Yaughanf has given the results of an 
examination of water supplies from various sources under 
the head of “Some Toxicogenic Germs Found in Drinking 
Water.” He uses for his work agar plates, one grown at 
the room temperature, the other at 38 degrees C. The tox- 
icogenic bacteria have their optimum growth at 38 degrees 
C., while many of the saprophytic water bacteria grow at 
lower temperatures. The pathogenic bacteria crowd out 
the saprophytic at a higher temperature. The colonies are 
counted at the expiration of twenty-four, forty- eight and 
seventy-two hours. Bouillon tubes are inoculated at the 
same time with like amounts of water. These tubes are 
kept in the incubator for twenty-four hours at from 38 
degrees to 40 degrees G. The temperature is not allowed 
to fall below 38 degrees C. If bacteria do not develop at 
this temperature it is regarded as safe. If bacteria are 
♦Hankin, E. H.— Centr. f. Eakt. 26:554. 
t Jr. of the American Medical Assoc. 42: i>85.* 
