LIMNOLOGICAL PROBLEMS 
39] 
Within later years a long series of investigations have been pub- 
lished: Davis (1900a, p. 485; 1900b, p. 498; 1901, p. 491), Wesenberg- 
Lund (1901, p. 1), Passarge (1901, p. 79), Frlih and Schroter (1904, pp. 
196-199), Weltner (1905, p. 277), Steusloff (1905, p. ] ), Marc le Eoux 
(1907, p. 347). We have all arrived at the same result, that the lime 
deposits are due largely, if not entirely, to organisms. Passarge (1901, 
p. 144) even maintains that these can cause lime deposits on a large 
scale. Ramann at first seemed to take up a special position. He 
believes " dass die Seekreide aus der Zersetzung geloster Kalkhumate 
hervorgeht welche dem Seewasser aus benachbarten Gebieten zuge- 
flihrt werden" (1905-6, p. 161; 1905, p. 44; and 1906, p. 174). 
Ramann has accepted the explanation of the origin of the true lake 
lime given by Passarge and myself, but seems still to maintain his 
own with regard to " Wiesenkalk,"' which he is no doubt entitled 
to do. I hope, however, to be able to return to this explanation later. 
It must therefore be concluded that Dr Krogh at present stands 
quite alone with his above-mentioned views. In my plankton work 
(1908, pp. 291-293), to which I here refer, I have contested the views 
of Dr Krogh. 
The " organism " which has probably most of all modified the 
natural conditions in the Baltic lakes is ma7i. In thickly populated 
territories, where castles and monasteries were often built near lakes 
and where towns arose under shelter of the castles, where later on 
water-mills and factories were worked by the effluents and affluents of 
the lakes, the lakes were drawn into his range of interest. Originally 
they were only of importance to man as fishing-grounds, later he 
learned to use parts of their vegetation (Phragmites and Scirpus) ; but 
after having destroyed the stock of fish, and the lakes had become like 
dead capital on his acreages, he utilised them in another way. The 
great desiccation projects began, and lake by lake disappeared ; in part 
through drainage, in part more indirectly through forest exploitation, 
a diminution of the lake area has in many places taken place. It 
must, on the other hand, be remembered that at possibly still more 
places man has kept the height of the water in the lakes above the 
normal level by means of locks and sluices. It is at any rate certain 
that the renewal of water in most lakes is dependent on the discretion 
of man. The comparatively small and shallow lakes with their often 
small affluents and outlets and their slight fall have made this possible. 
No less has he influenced the chemical composition of the lake-water. 
Substances alien to the latter (chlorine and ammonia) are in increasing 
quantities conveyed to it through the refuse from towns and the 
chemicals from factories (see especially Marsson, 1903, p. 60, 1904a, 
p. 1, 1904b, p. 125; Kolkwitz, 1905, p. 1, 1906, p. 370, with list of 
literature). 
