Nelson: some ai.o.e which cause ''water bloom." 55 



thin watery contents. The gonidia were still larger, were sur- 

 rounded by a thick wall and contained numerous granules of 

 different sizes. When floating naturally in the water, each 

 trichome of Anabcvna circinalis coils itself into a loose spiral — 

 hence its name. The trichome of A. flos-aquce, on the other 

 hand, is somewhat curved but not in a definite way. 



These plants in moderate quantities are not supposed to be 

 dangerous, but when they are present in immense numbers in 

 stagnant water they are likely to have an injurious effect. 



In 1897 Messrs. D. D. Jackson, Assistant Biologist, and J. 

 W. Ellms, Assistant Chemist of the Massachusetts State Board of 

 Health, made a series of chemical experiments on living plants of 

 Anabcena circinalis collected from Ludlow Reservoir, at Spring- 

 field. " It is commonly believed by those who have not investi- 

 gated the subject, that disagreeable odors and tastes in drinking 

 waters are due to the decomposition of organic matter, and are 

 either dangerous or indicative of danger to the public health. 

 Biological investigations already published have sufficed to show 

 that this is not always the case." 



The plant under investigation proved to contain an essential 

 oil giving the order of mouldy grass which is characteristic of 

 the genus. 



A chemical analysis was also made of the same plant in a 

 state of decay and showed that " the odor of decomposing An- 

 abepna is evidently not due, to any extent, to the production of 

 hydrogen sulphide, but to the partial breaking down of highly 

 organized compounds of sulphur and phosphorus. The odor is 

 undoubtedly more offensive on account of the high per cent, of 

 nitrogen present. It is true of the whole organic world that 

 those products which give the most offensive odors of decay are 

 partiallv decomposed, highly nitrogenous compounds, contain- 

 ing sulphur or phosphorus.'' 



The investigators concluded that the usual cause for disagree- 

 able odors and tastes occurring in potable water is found in the 

 presence of large numbers of certain microscopical organisms 

 which secrete compounds of the nature of essential oils. When 

 the organisms are living these tastes and oders are as harmless 

 as those of fresh vegetables or fish. When decaying, the plant 

 produces the " pig-pen " odor (characteristic of blue-green algae, 

 Cyanophycege) due to the decay of highly nitrogenous organic 

 matter in which partially decomposed sulphur and phosphorus 



