CULTUilE OF PLANKTON DIATOM TllALASSIOSIRA GRAVIDA CLEVE. 433 



experiment was carried out. 100 c.c. of a 1 per cent solution of peptone 

 in artificial sea-water was sterilized by boiling on successive days. When 

 cold it was inoculated by adding two drops of tank water. Under the 

 influence of the bacteria of the tank water putrefaction set in and was 

 allowed to continue for nineteen days. The solution was then again boiled. 

 To 75 c.c. of artificial miqueled sea-water three drops of the putrified pep- 

 tone solution were added, and the flask boiled, and when cold inoculated 

 with two drops from a culture of Thalassiosira in artificial miqueled water 

 plus 4 per cent of outside sea-water. At first the water in the culture flask 

 became milky from the growth of bacteria, but this milkiness gradually 

 disappeared and the diatoms commenced to grow, giving finally an 

 excellent culture which was quite up to the control. I do not think 

 there w^as any flaw in the actual carrying out of the experiment, but, 

 as already mentioned, a number of attempts to repeat it all gave nega- 

 tive results. 



A final point may be mentioned, which also seems to suggest some 

 organic substance as the missing factor which the artificial miqueled sea- 

 water must contain before it will sustain a vigorous growth of the diatoms. 

 It has been noticed that artificial miqueled sea-water which has been 

 kept for some weeks gives (without any addition of natural sea- 

 water) more growth than does similar water used within a few days of 

 being prepared. Plate-culture tests have shown that such water after a 

 few days develops bacteria, and it is possible that the products of the 

 metabolism of these bacteria are able to help the growth of the diatom. 



The Omission of Miguel's Solutions. If 4 per cent of tank water 

 (i.e. water from the Laboratory tanks, which are worked on a close 

 system of circulation *) be added to artificial sea-water, made according 

 to the formula already given, but to which neither of the Miquel solutions 

 is added, a good growth will result after sterilization and inoculation 

 with Thalassiosira. This growth may for the first week or two be quite 

 as good as a similar culture to which the Miquel solutions have been 

 added, but it will not continue healthy for as long as the latter, so that 

 the total growth will be less. It is interesting to note that the mere 

 dilution of the tank water with pure artificial sea- water produces an 

 increase of growth, for the amount of growth obtained in say 100 c.c. 

 of sterilized tank water is less than that obtained in a mixture of 

 96 c.c. of artificial sea-water with 4 c.c. of sterilized tank water. This 

 is partly explained by a difference in alkalinity, but it also suggests 

 that the tank water contains not only an abundance of the food sub- 



* Of. Allen and Xelson, loc. cit., p. 430, et seq. {Q.J. M.S., p. 373]. 



NEW SEKIES — VOL. X. NO. 3. OCTOBER, 1914, 2 B 



