IOWA- ACADEMY OF SCIENCES. 
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000 to 50,500, and from 829,000 to 78,500, respectively. It is 
thus evident that the bacteriologist must not only see to 
the collecting of his own samples, but must be intimately 
acquainted with their history until they reach his labora- 
tory. 
A further precaution that should be taken in making an 
analysis is the proper plating and the amount of dilution. 
We have found in ordinary practice of wells that tV of a 
c.c. of water is sufficient. The melted agar is poured out 
on the plate and the water is added to it. Then by gently 
tilting the plate backward and forward an even distribu- 
tion of the germs is obtained. The same method is used 
in gelatin plates. The gelatin plates harden less rapidly 
and hence a better distribution will be obtained than on 
agar, care, of course, being used when the plates are poured 
that there is no dust in the room, that the ends of the 
tubes shall be run through flames so that no germs will 
adhere when the agar is poured into the Petri dishes. For 
river water, especially if strongly polluted, it is necessary 
to dilute about ten times although this may have to vary. 
It is not advisable to have the plate covered with colonies 
as the different colonies are inimical to their development. 
The following is the result of our analyses of wells sup- 
plying the college boarding houses. The shallow wells are 
marked S. 
