CULTIVATION OF DIATOMS. 47 



These solutions are kept separately; for use add 40 drops of A and 

 20 drops of B to a litre of ordinary water, in which has been previously 

 placed 5 centigrs. of bran, 1 decigram of straw and a little quantity 

 of ground moss previously washed in boiling water. When made in 

 small quantities the cultivations are prepared in wide-necked flasks, 

 stoppered with a plug of loose cotton wool. Large cultivations are made 

 in crystallizing pans, &x. We have successfully employed square vessels 

 which had been previously used as electric accumulators. 



It is well to take the precaution of sterilising all liquids by heating 

 them in a water bath for a quarter of an hour, at a temperature of 

 about 70 (a), so as to destroy any spores or fragments of Algae or 

 even foreign diatoms, which those liquids may happen to contain. 



The cultivating liquid being ready it is fertilised by introducing 

 into it a few healthy frustules. 



The cultivations should be kept screened from the direct rays of 

 the sun. The best results are obtained by exposing the flasks to a 

 northern illumination, and keeping them at a temperature of io to 30 (c). 



When green Algas are produced their growth can be stayed by 

 diminishing the light. 



Diatoms will also flourish in artificial light, such as gaslight, &c. 

 Every 10 or 15 days fresh sterilised water, such as has been previously 

 mentioned, should be supplied in the place of any water which has 

 evaporated. 



If the cultivations "drag" (i.e.) develop slowly, this can often be 

 remedied by adding a few drops of solutions A and B in the before- 

 mentioned proportions. 



B. Artificial Cultivation of Marine Diatoms. 



The Cultivation of Marine diatoms may be favourably effected 

 in natural sea water. If this cannot be conveniently obtained, artificial 

 water should be used and this can be made by dissolving : 

 Sea salt ... ... ... 250 grammes. 



Magnesium Sulphate ... 20 



,, Chloride ... 40 



which should be dissolved in a sufficient quantity of water to make 

 up one litre of solution. The liquid thus obtained is subsequently 

 mixed with 9 litres of water immediately before using. 



The sea water is added to solutions A and B just as in the case 

 of the fresh water, and similarly sterilised at a temperature of 7oc. 



