60 



PROBLEMS OF LAKE BIOLOGY 



curring mostly as colloidal material, and its 

 deposition in the bottom. There is much 

 evidence that this material is not easily 

 decomposed by bacteria, that it is qnite dif- 

 ferent from the organic matter deposited in 

 eutrophie lakes. Indeed, there is a sugges- 

 tion that it is slightly antiseptic. Further 

 characteristics of such lakes, important 

 from a bacteriological standpoint, are the 

 sharp stratification with the thermocline at 

 or near the surface ; the often strongly acid 



numbers and kinds of bacteria characteris- 

 tic of each type. 



Table XI presents a summarj" of available 

 data on the relative numbers of bacteria in 

 eleven lakes, grouped according to types. 

 It is not pretended that these data are ade- 

 quate for any final conclusions ; many more 

 lakes will have to be studied, and more ob- 

 servations will need to be made on each lake. 

 The data may serve, however, to indicate 

 roughly what may be expected from further 



TABLE XI 



Comparison of Numbers of Bacteria in Different Lakes. 



1 Bacteria per square mm per day deposited upon slides. 



2 Colonies per cc of water on agar plates. 



3 Bacteria per cc of bottom mud on agar plates. (From Henrici and McCoy, 1938.) 



4 Bacteria per cc of water computed from counts of evaporated samples. (From Bere, 1933.) 



reaction, and the failure of light to pene- 

 trate through the deeply colored water. 



These facts and theories indicate that 

 both the quantitative and qualitative char- 

 acters of the bacterial flora must be ulti- 

 matel}' considered in the study of lake types. 

 While a number of observations on the oc- 

 currence of bacteria in different types of 

 lakes have been published, these observa- 

 tions have been so fragmentary, and have 

 been made by means of such diverse tech- 

 niques, that it is impossible to summarize 

 them and draw conclusions concerning the 



studies, and to indicate something regard- 

 ing the adequacy of the techniques used. 



Brazelle Lake is peculiar, and cannot be 

 readily fitted to the usual classification of 

 lakes. It is small, really a pond rather than 

 a lake. It occurs in the course of a brook 

 which brings in dark brown bog water. The 

 lake is only 2 meters deep, surrounded by 

 marshy ground. The bottom is a mass of 

 decomposing coarse plant remains, with 

 considerable fine material resembling "dy. " 

 The water is quite turbid. This lake was 

 selected for observation because of the large 



