90 THE AMERICAN MONTHLY [May, 



liability exists whenever a water supply is contaminated with human excreta, 

 and biological analysis, in the great majority of cases, is simply one means 

 of determining whether such contamination exists. As yet the microscopical 

 section has not undertaken to make the modern culture determination of the 

 number of bacteria present per unit of volume of water. The section, how- 

 ever, has at least two members who are qualified to conduct such examina- 

 tions, and it is expected that during the present year a series of such cultures 

 will be made, the results of which will in due course be laid before you. 



' Of the fresh-water alg£e, including the desmids and diatoms. 73 forms are 

 known to exist, and of these 10 classify with the desmids and 39 with the 

 diatoms, leaving 24 which belong with the filamentous and such unicellular 

 forms as are not included with the diatoms and desmids. 



' The desmids may be dismissed with a few words. So far as known they 

 have no special significance, being found in water of nearly all degrees of 

 purity. They have never yet been seen in Hemlock water in quantity. 



• The diatoms are represented by a large number of species, and manv of 

 the species by many individuals. At times a brownish scum is found around 

 the margin of the lake, consisting of innumerable quantities of these little 

 plants. They are not known to be in any degree prejudicial to health, though 

 without doubt they are occasionally the cause of certain bad smells found in 

 various waters. 



' Of the fresh-water algte. the most of them are of the grass-gi'een varieties, 

 and, generally speaking, cannot be considered as possessing any specially dele- 

 terious properties. A few species, however, may be noted as an exception 

 to this rule, as for instance, Conferva bombycitza^ is frequently met with as 

 a ^-ello wish-green, cloudy stratum in stagnant water. This alga has narrow 

 thread like filaments with the cells from four to five times as long as broad. 



' JVastoc piscinale., SphcErozyga polyspcnna^ and three species of Oscil- 

 laria, which have been identified, are of special interest bv reason, not onh 

 of their possible relation to the bacteria, but because of their having been 

 concerned in serious troubles which various water supplies have experienced 

 at different times. These plants are farther closely related to the anabtenas, 

 which are specially liable to give rise to unpleasant odors and tastes when 

 undergoing decay. 



' The nostocs are farther of interest in this connection as being the chief 

 source of the unpleasant smell known as the pig- pen odor. 



' It is matter of congratulation, therefore, that thus far these species have 

 been seen in Hemlock water, with one exception, in very small quantity. 

 The single exception is an oscillaria^ present about a year ago in consider- 

 able quantity, but which was not at that time, so far as known, the cause of 

 any unsanitary condition of the water. 



' This matter of the relation of plant forms to unsanitary conditions is not 

 only of the greatest interest from the sanitary point of view, but it, farther, has 

 important bearings to the student of cryptogamic botany, and certain questions 

 as to mode and period of recurrence may possibly be settled by such a long- 

 continued series of systematic observations as this section has undertaken. 



' The above is a fair exhibit of the microscopic fauna of Hemlock lake so 

 far as it has been elucidated up to the present time. By the end of another 

 year we hope to be able to lay before you many facts of interest, of which at 

 the pixsent time the significance has not been made out. Moreover, the con- 

 clusions of this paper, so far as we express any, must be considered as some- 

 what provisional and subject to revision if additional study shall seem to 

 justify the same.' 



Several conclusions deduced from the study are stated thus : — 



First. That Hemlock lake water as it comes to the city contains not only 



