231 



throughout the year, and it may be that some of the seasonal 

 fluctuations in the chemical substances which have been dis- 

 cussed in the preceding pages, and some of those in the plank- 

 ton also, depend in some measure upon this changing effect of 

 temperature upon the sewage. 



The following table, taken from Jordan ('00), gives the 

 seasonal changes in numbers of colonies of bacteria from May 



Bacteriological Examination of Illinois River at Havana. 



Date 

 1899 



Chlorine 

 (pts. per mil- 

 lion) 



Stage of 

 river, in feet 



Temperature 



of 



water. C. 



No. of colonies per cm 8 



Havana 



Pekin 



May 30 

 June 6 



13 

 20 



28 



July 5 



12 



19 

 26 



Aug. 9 

 23 

 30 



Sept. 6 



14 

 20 

 27 

 Oct. 4 

 11 

 18 



25 



Nov. 1 



15 

 22 



29 

 Dec. 6 



20 



13.6 



13- 



I3.5 



12.1 



14.9 



14.7 



23- 



36. 



3i- 



27.5 



34- 



39- 



40. 



46. 



35- 



49- 



52. 



59- 



58. 



60.5 



63. 



5'- 



47-5 



43- 



35- 



35 



8.7 



9-3 

 8.8 



7-5 

 5-2 

 4-7 

 4.1 

 4.9 

 4.8 

 4.1 



3- 



2.2 

 2.4 



2-5 



3-5 



3- 

 3- 



3-2 



3-2 



3- 



3-5 

 3-7 

 4.4 



4- 

 3-i 



4.8 



21 

 26 



25 

 26 



25 

 26 

 26 

 27 



30 

 26 

 26 

 29 

 29 

 22 



14 

 16 

 14.5 

 16. 



17 

 12 



9 

 10 

 11 



6 



2 



1 



4,500 



18,450 



15,900 



2,500 



4,500 



2,400 



7,300 



5,700 



850 



i.55o 

 900 

 9,800 

 1,900 

 1,500 

 3.400 

 3.700 

 2,500 

 6,600 

 8,8oo 

 3.900 

 7,000 



3.3oo 



128,000 



41,600 



85,000 



66,800 



542,000 

 129,000 

 205,000 

 225,000 (1) 



2,030,000 (2) 

 52,000 (3) 



1,435,000 

 470,000 (4) 

 980,000 (5) 

 985,000 (6) 

 10,000 (7) 

 30,000 (8) 

 650,000 (9) 

 310,000 (10) 

 240,000 (11) 

 120,000 (12) 

 500,000 (13) 

 430,000 (14) 



30,000(15) 

 150,000 (16) 

 30,000 

 1,650,000 

 380,000 (17) 

 140,000 (18) 

 5,000 



(1) June 21. (2) June 27. (3) July 6. (4) July 18. (5) July 25. (6) Aug. 8. (7) 

 Aug. 22. (8) Aug. 29. (9) Sept. 5. (10) Sept. 12. (11) Sept. 18. (12) Sept. 26. (13) 

 Oct. 3. (14) Oct. 10. (15) Oct. 31. (16) Nov. 7. (17) Nov. 30. (18) Dec. 5. 



30, 1899, till the end of the year at Havana, and at Pekin, 

 thirty-two miles above. The decline from the larger numbers 

 in June to a fairly well-maintained minimum during midsum- 

 mer at Havana is very evident, as is also the rise as the tem- 

 perature lowers in the autumn. Both the period of time and the 



