SYMPOSIUM ON SAXITATIOX 47 



water bearing stratum. We therefore find many of the cities 

 in this area obtaining their water supplies from wells from 

 100 to 200 feet in depth. These waters are also prefectly free 

 from contamination in the water bearing strata and if proper- 

 ly cared for, furnish a perfectly hygienic supply. 



In the western part of this area and to the south of a line 

 drawn from St. Louis to Danville, the drift is not deep enough 

 to furnish sufficient reservoir capacity and it is necessary to 

 rely on surface waters for municipal supplies. Very few of 

 the surface water supplies in this section of the state have 

 been filtered. The unfiltered water supplies are not only un- 

 attractive for drinking but they may be contaminated or even 

 infected. With unattractive municipal supplies the citizens 

 in this section use water from shallow wells which may be 

 impure. 



Under such conditions we expect a higher typhoid fever 

 death rate in the southern part of the state than in the east 

 central and northern parts. 



A study of the statistics collected by the State Board of 

 Health from 1904 to 1^11 {*) shows this to be the case. Divid- 

 ing the state into two parts, (see map) 51 counties to the north 

 and the same number to the south. Ave find in the northern 

 part of the state but two counties with a rate exceeding 30 

 per 100.000 and not one county with a typhoid fever death 

 rate of 40 per 100.000. Sixteen of these northern counties had 

 a rate of below 10 per 100.000. 



In the southern part of the state there were five counties 

 with a typhoid fever rate of more than -K) per 100.000 and 12 

 more with a typhoid fever death rate of more than 30. and but 

 one with a rate below 10 per 100.000. It is gratifying to note 

 that the average for the eight years. 1904-11 is better than the 

 average for the five years 190-^-8. 



Another reason for typhoid fever in the southern part of 

 the state is the fact that 52 per cent of the towns of more 

 than 1.000 inhabitants have no water supply, whereas in the 

 northern part only 10 per cent are without a water supply. 

 Shallow wells are of course used where there are no municipal 

 water supplies and it is certain that the use of shallow well 

 water is influential in spreading typhoid fever. 



We have carefully classified all well waters sent to the 

 Survey for examination during the years 1907-12. The waters 

 received have been classified according to depth as follows : 

 Less than 25 feet. 25 to 50 feet. 50 to 100 feet, over 100 feet, 

 and unknown. The variation in the quality of each class from 

 vear to vear is but slight as indicated on the diasrram. The 



♦Proceedings Illinois Water Supply Association. 2, 151-164. 



