Highly Organized Flora of Running Streams. 9 



on the question of the self-purification of streams exami- 

 nations of polluted waters have shown that the organisms 

 which predominate in these waters are the chlorophyl-free 

 organisms. Experiments have shown that these are cap- 

 able of existing upon organic matters such as found in 

 these polluted streams. Certain forms have been found 

 more constantly than others ; appearing to possess a pre- 

 dilection for such water. For instance, Pfeiffer and Eisen- 

 lohr (Archiv fur Hygiene, Bd. 14, p. 90, 1892) in their 

 investigation of the river Isar found large quantities of a 

 particular form of beggiatoa. Samples of water collected 

 at different points of the river were found to contain 

 enormous quantities of active growths of beggiatoa roseo- 

 persicina (Zopf). Between the threads of this organism, 

 however, other fission fungi were found in enormous num- 

 bers, as yeast, diatoms, protozoa in fact, all possible forms 

 of lower vegetable and animal life forms, however, which 

 were not examined further because they had no signifi- 

 cance with regard to the question under consideration. 

 From their investigations it seemed evident that this 

 particular variety of beggiatoa was present only in polluted 

 waters, and did not penetrate into the fresh water streams 

 entering the river ; its great prevalence at any point 

 appeared to indicate the presence of undue quantities of 

 organic matter. 



Schenk (Centralblatt fur allgemeine Gesundheitspflege, 

 12. Jahr., p. 365, 1892) in his investigation on the signifi- 

 cance of the Rhine vegetation in the self-purification of 

 the river, reports on several forms of algae found adhering 

 to the stones along the banks in large quantities, which 

 seemed to him to have some influence upon the purification 

 of the river. Among the chlorophyl-free plants he says 

 that the saprophytic water plants of the first and greatest 

 importance are the bacteria. The two forms which he 

 says require special consideration, from the large numbers 

 found, are the beggiatoa alba and the cladothrix dicho- 



