90 SHELLFISH CONTAMINATION FROM SEWAGE-POLLUTED WATERS. 
The length of time required for this cleansing process to be thor- 
oughly accomplished undoubtedly varies according to local condi- 
tions. At least one month should always be allowed for this change 
to take place, although an entire season would be preferable. 
Tables 5 and 6 show the sharp contrast between the bacteriological 
findings on water and oysters from sanitary and insanitary grounds. 
TaBLeE 5.—Bacteriological examination of water and shellfish collected from grounds 
below the sewer shown in figure 1. 
SHELLFISH. 
| 
| Bacteria per cubic 
centimeter (plain : 
agar incubated | B. coli 
| 
| Sample four days). per cubic : pene 
NG: our days) ventie Salt. Remarks. 
SS ef Be) 
25° C. | Slime: 
| Per cent. 
1 ee eae 6, 000 6,000 | LOO ote es aos Polluted. 
2-2 =| 407000 30, 000 1, 000 Mass Soe ee. | Badly polluted. 
WATER. 
Lee oes | 900 700 10 1.19 | 1 mile from sewer. 
Deena | 6,800 2, 000 1,000 -13 | 100 yards from sewer. 
Stee ete 1, 800 700 1,000 -10 | 300 yards from sewer. 
| 
Extensive industries are being operated from the locality in which 
these samples were taken, and the products are widely distributed. 
The data given in Table 5 should be compared with the following 
results obtained on shellfish and water taken from clean grounds: 
TaBLE 6.—Bacteriological examination of water and shell fish collected from clean grounds. 
SHELLFISH. 
Bacteria per cubic 
centimeter (plain ; 
| agar incubated| B. coli 
Sample four days).. | Percubie) salt. Remarks. 
No. | centi- 
| meter. 
25° C. Sige 
Per cent. 
1 Boeaeceas 8, 000 300 (al Pale ait No pollution. 
DV 8, 600 5, 000 Org eee sees Do. 
Beer ae | 6,800 3,000 Oimslea ser eee Do. 
7 eet eee 500 50 OMI see ee Do. 
WATER. 
West t se 300 | 100 0 2.84 | 16 miles from land. 
SGT AEN 1,200 500 0 2.86- | 3 miles from land. 
Shee 300 20 0 2.88 | 5 miles from land. 
FLOATING OYSTERS IN POLLUTED WATER. 
INSPECTION DATA. 
When shellfish grounds are properly located with regard to sewage — 
disposal, it is not an uncommon practice to nullify the cleanly results 
obtained by taking oysters from beds free from pollution and float- 
