432 E. J. ALLEN. 



instances in which some growth was obtained it was distinctly below 

 that of cultures of the former series made at the same time. 



A study of Table A can, I think, leave no doubt that the general 

 statement is justified that whatever the substance may be which occurs 

 in tank water and the addition of which to artificial miqueled sea-water 

 enables the latter to support a vigorous diatom gro^vth, that substance 

 may be dried and heated to a moderate degree without greatly impairing 

 its efficacy, whilst if it is heated to too high a temperature its efficacy 

 tends to be destroyed. 



The experiments are consistent with the theory that the substance 

 is an organic compound, but one of a very stable kind, which is only 

 decomposed with difficulty. 



Addition of organic substances to artificial water. Many experiments 

 have been made by adding organic substances in a number of different 

 concentrations to artificial miqueled sea-water, but by none of these has 

 any marked or constant effect been produced upon the growth of Thalas- 

 siosira. It will be understood, of course, that such negative results are in 

 no way conclusive, as in a case of this kind the attainment oi an exactly 

 correct degree of concentration may be essential, and when one is working 

 quite without clue it is hardly possible to carry out a sufficiently extensive 

 series of experiments with every substance, especially when two or three 

 weeks must elapse before the result of any experiment becomes definite. 

 The following substances have been tried : asparagin, calcium succinate, 

 calcium malate, sodium salicylate, theobronine, leucine, tyrosine * (the 

 three latter alone and together with atropine), f peptone, urea and uric 

 acid. In all cases the result was negative. 



Putrified Peftone. An isolated result which I have entirely failed to 

 repeat in spite of many attempts may be worth putting on record as a 

 hint for future work, but no other importance should be attached to it. 

 Starting from the idea that the substance sought for might be one of the 

 ultimate products of the breaking down of organic matter under the 

 influence of bacteria, since it appears to be more abundant in the tank 

 Avater of the Laboratory than in sea-water from outside, the following 



* In consequence of the work of Thornton and Geoffrey Smith on Euglena {Proceed. 

 Roy. Soc, B., Voh LXXXVIII, p. 151, 1914) special attention was given to tyrosine, and a 

 arge number of diff"erent concentrations were tried. Entirely negative results were, how- 

 ever, obtained. 



t The use of these three substances alone and with atropine was suggested by the work 

 of H. C. Ross on "Auxetics." See H. C. Ross, Induced Cell- Reproduction and Cancer, 

 London, J. Murray, 1910 ; Further Researches into Induced Cell-Reproduction and Cancer, 

 I and II, London, J. Murray, 1911 and 1912. 



