126 
IOWA ACADEMY OF SCIENCES. 
The conviction has grown on us that none of the Iowa 
wells are absolutely free from bacteria. Generally speak- 
ing, the deep wells contain less organisms than the shallow. 
Prescott and Winslow* conclude that “it is plain that 
water absolutely free from bacteria is not ordinarily ob- 
tained from any source and that even deep wells contain 
quite appreciable numbers.” They find that the bacteria 
from deep wells show a slow development at room temper- 
ature, “the entire absence of liquefying colonies and the 
abundance of chromogenic bacteria.” In our investigation 
two types of wells have been examined. (1) The shallow 
which are usually bricked or tiled. They rest on a blue 
clay. (2) Tubular wells varying in depth from 60 to over 
100 feet. In the vicinity of Ames they have gone through 
the Wisconsin drift. The plates were not incubated but they 
were plated in a covered case and counted in 48, 72 and 
120 hours. Duplicate plates were poured in each case. The 
older the well the greater are the number of bacteria. It 
is also evident that there are many interesting problems 
in connection with a study of our water supplies. 
* Elements of Water Bacteriology. 18. 
