294 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



of silk cloth, of different sized meshes. A great difficulty 

 in the chemical investigation method is the getting rid 

 of the salt water which adheres to the organisms. In the 

 filter most of the water filters through, bnt a certain 

 amount invariably remains behind. The difficulty may 

 be avoided in two ways, either by washing the organisms 

 on the silk cloth with fresh water or by making, by means 

 of a chlorine estimation, an estimate of the amount of 

 salt retained on the average in a catch of given volume 

 or weight. The former method is the more successful one. 



For the dry weight estimation the total catch is first 

 of all dried in a water bath at a temperature of 100° C. 

 Then it is placed in a desiccator containing strong 

 sulphuric acid until the weight becomes constant. Then 

 it is weighed by means 'of a Bunge's balance to the nearest 

 0-0005 gram. 



The analytical methods consist of (1) Estimation of 

 carbon and hydrogen. 2. Estimation of nitrogen. 3. 

 Ether extract. 4. Estimation of ash. 5. Estimation of 

 chlorine. C. Estimation of silica. Occasionally the 

 quantity of chitin, cellulose or the soluble carbohydrates 

 were estimated. A detailed consideration of these methods 

 is beyond the scope of the present summary. 



The last and perhaps the most satisfactory method of 

 investigation is that of the enumeration of the individual 

 constituents of the plankton. This method gives us a far 

 better idea than any other of the nature and variability of 

 the plankton. It is obviously impossible to count all the 

 individuals of the catch, as the following facts prove. On 

 one occasion Hensen found in one cubic metre of water 

 from Kiel harbour 13 million individuals of Ceratium 

 tripos, and on another occasion 102 million Rhizoso- 

 lenia semispina. In the first place the excess of 

 the preservative fluid is decanted off, and the 



