96 MICRO-OEGANISMS IN WATER 



The time occupied by the Isar in flowing from Munich 

 to Freising is about eight hours, and in this time, there- 

 fore, by far the greater proportion of the organisms 

 introduced into the river at the point of the sewage 

 outfall disappear. 



Since the experiments on the Spree by Frank, and 

 those on the Isar by Prausnitz, an exhaustive investi- 

 gation has been made by Schlatter ^ of the variations 

 in the bacterial condition of the river Limmat before 

 and after it receives the drainage of Zurich. As in 

 the above experiments, various spots along the river's 

 flow were selected, and a series of samples collected and 

 submitted to plate-cultivation. The observations were 

 made during the months of January to April 1889, 

 and the following were the places chosen for the 

 sampling of the water : — 



(1) Stadtmiihle. This is pure Limmat water, and is just above the 

 influx of the sewage. 



(2) Left current of drainage water after admixture \ 



with the river, about 40 metres 



(3) Middle current of drainage water after admix- below the en- 

 ture with the river, ( trance of the 



(4) Eight current of drainage water after admix- drain, 

 ture with the river, / 



(5) Water coming from the Hardmiihle about 450 metres lower down 

 than Nos. 2, 3, and 4. 



(6) Hard Fahre about 300 metres lower down than No. 5. There is 

 a silk factory between this and No. 7, but experiments showed that the 

 bacterial disturbance caused by it was insignificant. 



(7) Hongger Briicke. 2J kilometres below Nos. 2, 3, and 4. 



(8) Engstringer Briicke. 4 kilometres below No. 7. 



(9) Kloster Fahrli. 600 metres below the bridge (No. 8). 



(10) Dietikon Fahre. lOJ kilometres below Nos. 2, 3, and 4. 



The whole distance covered hj the investigations, 

 from the Lake of Zurich to Dietikon, is 14 kilometres. 



^ * Der Einfluss des Abwassers der Stadt Zurich auf den Bacterien- 

 gehalt der Limmat,' by Carl Schlatter. Zeitsclwift filr Hygiene^ vol. ix, 

 p. 56, 1890, 



