1888.] MICKOSCOPICAL JOURNAL. 89 



entirely made up of se^vage, and in the mud along the margins of these streams 

 Tubifex may be found in vast quantity. The more offensive the stenches 

 arising from the deposited sewage the greater the probability of finding Tubi- 

 fex. Several times I have seen the mud margins of these streams completely 

 covered for many hundred feet with this unpleasant creature. Their red color 

 enables one to easily distinguish them, and it is an interesting experiment 

 to disturb a colony and observe how quickly they withdraw from observation 

 into the mud. From a histological point of view Tubifex is of the greatest 

 interest, as its transparency is such as admits of a detailed stud}' of the most 

 minute structui'e of the living worm. 'We may learn all the mysteries of its 

 life, see its two hearts, its large liver, its blood-vessels, its nervous centres, 

 and, indeed, its whole nervous and circulatory sj'stem.' Its presence in anv 

 quantity could be safely taken as evidence of sewage contamination. 



Of the rotifera 30 species are known to exist in Hemlock lake water, and 

 many of them are of interest from every possible point of view. 



Plumatella^ Pa/udicella^ and Christatella are the three representatives of 

 the fresh-water polyzoa thus far identified. Our president has made a special 

 study of these animals, and has watched the development of Plumatella from 

 a few individuals to a numerous branching colony, consisting of hundreds. 

 Generally they may be looked for in waters containing decaving matter, and 

 Johnson says of one species, not, however, found in Hemlock lake, that it 

 occurs in stagnant waters, especially such as are tinctured with iron in solu- 

 tion. Their presence in Hemlock lake water must also be taken as indicating 

 at any rate a moderate degree of contamination. 



ENTOMOSTRACA. 



Fourteen species of entomostraca have been recognized, and several of them 

 are found at different seasons in great quantity. A knowledge of these little 

 animals is of the greatest importance, not onlv because of their unparalleled 

 numbers, but because of their intimate relation to what maybe termed _o-rt>^'j- 

 organic infection. They serve not only as food for many species offish, but 

 they also serve (being themselves enormous gluttons) as devom^ers of that 

 which if left in the waters they inhabit would become the source of devasta- 

 tion and death. Referring to this group, C. L. Herrick, the American au- 

 thority, says : — ' The animals of the above group are, it is likely, the best 

 criteria by which to judge of the purity of natural waters, if their distribution 

 were correctly understood. A critical study of the contents of samples of 

 such waters will enable us to determine their character almost as well as by 

 analysis.' 



The entomostraca substantially conclude our list of life residing in Hem- 

 lock lake, and we may now turn to the protophyta ; and among these, as 

 being lowest in the scale, we will first consider the bacteria. Several species 

 have been seen, but whether they belong to the septic or pathogenic forms 

 we have no means of determining. At any rate, the conditions about Hem- 

 lock lake are such as 'to render the presence of pathogenic bacteria at times 

 by no means improbable. The stimulating effect of the dissolved phosphates 

 and nitrates of commercial fertilizers has vast importance in relation to the 

 possibility of the presence in Hemlock water of the pathogenic bacteria. 

 These substances are found to be the natural nutrients for bacterial life, and 

 their presence even in very minute quantity would be liable to lead to serious 

 consequences. A recent editorial in the Satiitary Engineer places the argu- 

 ment so appositely in its application to the conditions at Hemlock lake that 

 I will cite the conclusions here. The editor says : — ' A dangerous water supply 

 is not merely one which actually contains specific pathogenic bacteria. It is 

 one which is specially liable at times — not always — to contain bacteria. This 



