IOWA ACADEMY OF SCIENCES. 
119 
They concluded as follows: “If we consider the results 
of this examination of the litmus-lactose agar plate it be- 
comes apparent that organisms capable of growth at the 
body temperature are not numerous in unpolluted waters; 
acid formers are practically absent.” 
In addition to these media we have used in our water 
investigation of the well supplies ordinary litmus agar and 
litmus gelatin, dextrose agar. None of these media have, 
however, been very satisfactory. The litmus agar and 
gelatin, and especially the dextrose contained as a rule 
less organisms than the gelatin. 
In order to get accurate data on water supplies especially 
from a bacteriological standpoint the bacteriologist should 
at least insist on collecting the samples himself, and under 
conditions which will guarantee a perfect sample. They 
should be plated as soon as possible after the water is col- 
lected. We can not insist too strongly on the statement 
made by G. E. A. Winslow * that “The extreme delicacy 
of the test renders imperative the utmost care in the tech- 
nique of bacteriological analysis; for a speck of dust, a delay 
of a few hours, or a mistake in the preparation of the 
nutrient gelatin, may introduce an error in excess of the 
normal difference between the purest and the most polluted 
drinking-waters. First, in the collection of the sample, it 
must be certain that the small portion taken represents 
fairly the whole body of water from which it is drawn. 
The first water flowing from the tap or a pump must be 
rejected, as it may have acquired impurities from the 
mouth of the faucet or of the spout. On the other hand, 
water which has stood all night in the service pipes of a 
house will be lower in bacteria than the supply from which 
it is derived. In a lake or pond the surface scum and bot- 
tom sediment must be equally avoided.” 
Bacteria begin to multiply more after the sample is 
collected. All of our waters contain sufficient nutrient 
material to cause such multiplication. 
♦Winslow, C. E. A. Jr. New Eng. Waterworks Assoc. 15 : 460. 
