438 E. J. ALLEN. 



suggest that the amido acid acts as an auxiliary or stimulant rather than 

 as' the main source of nutrition. This view is similar to that taken by 

 H. C. Ross in his work on Induced Cell-Reproduction and Cancer, to 

 which reference has already been made (see p. 4.32). 



It would seem that the plankton diatoms, the culture of which has been 

 considered in the present paper, show a phenomenon of a similar character 

 to those just mentioned. The minute trace of substance added to the 

 culture medium in the small percentage of natural sea- water would seem 

 to act as a catalytic agent, initiating the processes of metabolism but not 

 being itself used up. 



The experiments may also help to throw light upon what takes place 

 in the sea. It is well known that the waters of the open ocean far from 

 land support a much smaller proportion of plant and animal life than is to 

 be found in coastal waters. On the other hand, in regions where a current 

 of coastal water meets and becomes mixed with a current of ocean water 

 conditions are produced which are specially favourable to a luxuriant 

 growth of animal and vegetable hfe. This is shown in the first place in 

 the very rich character of the plankton, and as a consequence of the 

 abundant plankton we find a rich fauna of bottom living organisms and 

 of fishes of different kinds. This is in agreement with the observation 

 recorded in the present paper that a small quantity of natural sea- water of 

 an inshore type (tank-water) mixed with a large proportion of pure 

 artificial sea-water gives a good culture medium for the plankton 

 diatoms. There is reason to hope therefore that culture experiments 

 may in time throw additional light upon the general questions relating 

 to the production of animal life in the sea, questions which are of 

 immediate importance to a study of the productivity of the fisheries. 



SUMMARY. 



1. Attempts to obtain good cultures of Thalassiosira gravida in a purely 



artificial medium, made by dissolving in doubly distilled water 

 Kahlbaum's pure chemicals in the proportions in which the salts 

 occur in sea- water, adding nitrates, phosphates and iron according 

 to Miquel's method and sterihzing the medium, have not succeeded. 



2. If, however, a small percentage of natural sea-water (less than 1 per 



cent will produce a result) be added to the artificial medium and 

 the whole sterilized excellent cultures are obtained, which are often 

 better than any which have been got when natural sea-water forms 

 the foundation of the culture medium. 



