6 
ance of the bottom-layers; the former had brown or gray deposits, the latter 
black and stinking. I therefore considered a more exact investigation of the 
deposits in our waters in high degree desirable, all the more as I have long 
known, that most of the lower animals in our fjords, which are not predatory or 
live on living plants, contained in their digestive tract a mass, which was nearly 
related or identical with the uppermost, brown layer covering the bottom 
of all our waters, where it is sufficiently deep and still for the fine particles 
to be deposited. I felt obliged to conclude, that this mass in the digestive 
tract of the animals composed their essential food and it was therefore 
of the greatest importance to know more precisely what its nature and origin was. 
This mass may be called dust-fine detritus; in addition to inorganic materials, 
it consists of a quantity of dead, deposited particles of plants and animals, among 
which we comparatively seldom find the remains of plankton organisms. »Living« 
microorganisms are naturally also found in the stomachs, but usually only in 
small quantity. We have so long and so often heard of the role the plankton 
is considered to play in the economy of the sea, that we almost forget the other 
sources of food, which however, at any rate in the smaller waters, certainly have 
an even greater importance. It seems to be time, therefore, that these sources 
were also investigated and estimated according to their value. An attempt in 
this direction will be made in the sequel. But just as the methods of plankton 
investigation have with time undergone extensive reforms, we may also expect, 
that our methods of investigation will become changed in much and many ways; 
what we report on here should rather be regarded as merely orientating investi- 
gations on an almost unworked field, where with new apparatus and new methods 
we have endeavoured to make a step forwards to an understanding of the meta- 
bolism of the sea, a subject first taken up by V. Hensen and later by K. 
Brandt in Kiel, but which none other, so far as I know, has attempted to 
carry further. 
These investigations have cost much time and trouble, chiefly owing to 
the great amount of experimenting one way or another, and without my assis- 
tants Cand. H. Sell and Magister H. Blegvad, as also the crew of the »Sal- 
lingsund«, they would naturally not have been accomplished. In Dr. P. Boysen 
Jensen I have found one whose knowledge supplements mine in many direc- 
tions; without his cooperation the matter would indeed not have. been carried 
very far. Professor W. Johannsen has afforded me assistance in working up 
the numerical material and has placed the Plant-Physiological Laboratory of 
the University at our disposal for making the necessary analyses, for all of which 
we owe him special thanks. The scientists of the Zoological Museum of 
the University have also assisted us in the determination of various animal forms 
and I would especially thank Professor H. Jungersen, Dr. Th. Mortensen and 
Docent Stamm for their cooperation. 
The sections II—IV have been written by Boysen Jensen, the rest by 
C. G. Joh. Petersen. 
Copenhagen, 12. February 1911. 
