Highly Organized Flora of Running Streams. 1 1 



spores, together with many other organisms in smaller 

 numbers. The change produced in the water by these 

 organisms made the water turbid and green, and conse- 

 quently unfit for drinking, on account of the taste, odor and 

 appearance. The nitrate compounds are rapidly trans- 

 formed by the organic growths, and it seems reasonable 

 to conclude that this means the destruction of substances 

 undergoing decomposition contained in the water." They 

 state further that " from a health standpoint this may 

 be classed as an instance of the self-purification of 

 streams, even though the water is temporarily rendered 

 obnoxious by the organisms which have effected the 

 change." 



Recently E. Goldschmidt, W. Prausnitz and others have 

 published (Hygienische Rundschau, 8. Jahrg., p. 161) an 

 important investigation on the death of micro-organisms 

 in the self-purification of rivers. Their experiments were 

 made upon the river Isar, making a continuous study of 

 the condition of the Isar from 1889 to the present time, by 

 themselves and other investigators. Samples of water 

 were collected at various points of the Isar below Munich: 

 for instance, at upper or lower Fohriug, at Ismaning, at 

 Freising, and at Landshut. In all these investigations it 

 was found that there is a uniform diminution in those 

 bacteria which grow on ordinary gelatine media, in regular 

 gradation as one proceeds down the stream. The following 

 results show fairly well the rate of diminution at the dif- 

 ferent points, and are taken from examinations made in 

 December, 1893, showing at Fohring 24,097 organisms 

 per cubic centimeter; at Ismaning, 15,065; at Freising, 

 7134, and at Landshut, 1976. 



As the result of their investigation they have reached 

 the following conclusions : 



i. The self-purification of rivers, as shown in the dis- 

 appearance of impurities, is not influenced by the activity 

 of micro-organisms. 



