26 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
purely scientific as well as from an economic point of 
view—belongs to the physiologist Piitter. It seems 
probable that in many cases organic compounds in solu- 
tion in sea water are utilised by marine animals as food in 
addition to solid matter. In the present course, 
however, it was maintained that further experiments 
are required to determine the relative amounts of food 
present in solution and as plankton in definite volumes 
of sea-water taken at different seasons. The amount of 
carbon in solution has been determined so far by direct 
analysis of filtered sea-water, whereas the quantity 
present as plankton has been determined by calculations 
from analyses of plankton catches. It should be quite 
simple to determine, by taking filtered and non-filtered 
samples of sea-water at the same time and place, and by 
carrying out direct analyses of these, whether the organic 
carbon compounds in solution are a more abundant source 
of carbon than the planktonic organisms. Dr. Dakin 
hopes to return to this matter in his future work. 
Dr. Roaf supplies the following note on the chemical 
and physiological part of the course :— 
‘“The chemistry of the sea-water was treated from 
the modern standpoint of physical chemistry, involving 
the question of ionisation and equilibria between the 
various constituents. 
‘* Estimation of chlorides was carried out by Mohr’s 
method as modified by the International Committee, 
using Knudsen’s pipette and burette. 
‘“‘“The oxygen in sea-water was determined by 
Winkler’s method as appliea by Natterer. 
‘‘ Methods for the estimation of carbon-dioxide are 
numerous, but the necessary steps are as follows :— (1) 
Liberation of carbonic acid by some stronger acid, (2) 
raising of the vapour pressure of carbon-dioxide by heat, 
