654 TRANSACTIONS OF SECTION I. 
MONDAY, SEPTEMBER 9. 
Joint Discussion with Section D on the Physiology of Aquatic 
Organisms. 
(i) The Nutrition of Marine Animals by Dissolved Organic Material. 
By Avaust Pirrer. 
The quantitative determination of the nutritive needs of the lower marine 
forms by means of metabolism experiments has shown that the views held at 
the present time, concerning their nourishment, need correction. ‘These forms 
are not nourished, at least to any great extent, by the suspended particles having 
their origin in marine plants, as has been assumed, but by the dissolved organic 
matter which is found in sea-water in great dilution and which is directly 
absorbed. The sea-water itself is therefore for these forms a nutritive medium. 
All recent investigation refutes the belief that the alge present suffice to 
nourish most of the prevalent plankton-animals, copepoda, and appendicularia. 
In the sponges, where long-continued metabolism experiments were made, it was 
demonstrated that suspended particles (only those of minute sizes are capable 
of passing through the pores) are incapable of supplying the nutritive require- 
ments of these organisms. The daily nutritive need at 12° C. amounts to about 
1 to 15 per cent. of the body weight. The same applies to the rhizostomea, 
in which, for anatomical reasons, the ingestion of larger particles is impossible, 
and which have a great food requirement (about 7 per cent. of the body-weight 
per day). Experiments on the actinia and ascidia have shown that dissolved 
organic matter is absorbed by these forms, and accordingly at the same time 
disappears from the sea-water. ‘The method employed was that of the dis- 
coloration of permanganate, a method which was employed by Natterer at the 
Mediterranean. Concerning the question of the origin of the dissolved nourish- 
ment, it was shown that there was a quantitative increase in the sea-water to 
which algze have been added, provided light is permitted to fall upon it; this 
nutritive material must, therefore, be considered as assimilatory products of the 
marine alge. 
(i) The Nutrition, Metabolism, and Respiration of Aquatic Animals. 
- By Brnsamin Moore, M.A., D.Sc., F.R.S., E>warp Wnuittey, 
M.A., Epwarp S. Epi, M.A., and W. J. Daxtn, D.Sc. 
It has been shown that marine animals cannot he nourished either by dis- 
solved organic matter, as supposed by Pitter, or by a process of fishing-out 
minute plankton, supposed to be uniformly distributed in the sea-water, but that 
they must search out either richer veins of plankton or feed on larger portions of 
vegetable or animal food along the littoral. The amount of dissolved organic 
inatter in sea-water is practically negligible, lying well below one milligram per 
litre of water. The plankton removed by silk bolting of 20-mesh, as usually 
employed for plankton tow nettings, removes only about 0.1 milligram per 
litre when the water is completely filtered through it, and a Chamberland 
candle removes about five to six times as much finer plankton, including 
bacteria. These two sources together do not usually exceed one milligram per 
litre. Estimations have been carried out to show the demand for oxidisable 
food of various species of invertebrates, and it has been found that while the 
plankton supply, as uniformly distributed, might prove sufficient for such species 
as sponges and ascidians, it is quite inadequate for crustaceans, molluscs, and 
echinoderms. The relative output of carbon dioxide as compared with intake 
of oxygen has been ascertained, and it is shown that complete oxidisation of: 
the food does not occur, the respiratory quotient lying well over unity in most’ 
cases. A metrbolic basis for accounting for this peculiar respiratory condition 
is put forward. 
