598 
The cultures arrived in good condition except in a few cases, and in 
every case it was possible from one or both Petri dishes to make a 
determination of the number of bacteria per 1 cubic centimeter of the 
water. 
It was found desirable to visit a certain number of dairies a second 
time after an interval of about four or five months from the date of 
the first visit, in order to check up and supplement the results ob- 
tained upon the first occasion. 
The results of the investigation are given in detail in a report to 
the chief of the Bureau of Animal Industry which also includes de- 
scriptions of the places visited with photographs of many of them. 
In general the results show that there were 140 places visited in 
Maryland and 15u in Virginia . Of the Virginia dairies, 53 were vis- 
ited a second time. At some of the dairies 2 different supplies were : 
used, either 2 wells or a well and spring or either of these and a 
cistern. More wells than either springs or cisterns are used and | 
more springs than cisterns. In Maryland there are 92 wells, 42 j 
springs and 14 cisterns. In Virginia 75 wells, 63 springs and 17 cis- 
terns. 
In assigning a rating from the sanitary survey, account was taken 
of the general lay of the land roundabout, the liability to pollution 
from seepage, and the liability to pollution by direct introduction of 
impurities down the shaft in the case of wells, and into the basin in 
the case of open springs. 
In pronouncing upon the presence or absence of pollution from the 
result of the chemical anal}^sis, it has been necessary to assume some 
limits for purity, and from various statements given in the books and 
from the experience gained in the present investigation a maximum 
of 0.01 parts per million for nitrates, 0.02 for free ammonia and 0.05 
of albuminoid ammonia were adopted as standards. The maximum 
allowed for chlorine varied of necessity" for different localities. In 
the Maryland dairies the maximum found in the well water free from 
suspicion was 47 parts per 1,000,000, the minimum was 5. 
In the Maryland springs otherwise free from suspicion the mini- 
mum amount of chlorine was 4 parts per 1,000,000, the maximum 6. 
In Virginia some of the wells which were free from suspicion showed 
as much as 63 parts per 1,000,000; while others showed only 5 parts 
per 1,000,000. Those in Virginia showing the larger amount lie in 
the region with Ashburn for a center and extending west to Leesburg 
and east to Herndon. In this district the minimum amount of 
chlorine was 11 parts per 1,000,000; the maximum 75. Outside of 
these limits the amount of chlorine averaged about 23 parts per 
1,000,000 in the wells which showed no evidence of pollution as far 
fls other criteria are concerned. 
