42 ON THE CULTIVATION OF DIATOMS 



golden«yellow spots of the best and most flourishing growths turn 

 green, then lose all their colour, and at the end of the day the 

 result is disastrous, all the diatoms have perished, and the liquid 

 in which they are placed gives out an aromatic odour of aniseed, 

 very like that of the bug. You may notice that in exposing to the 

 action of the sun-light, two vessels, one containing a growth of 

 diatoms and the other distilled water, that the temperature of the 

 hquid containing the organisms may rise to 48^ and 50°, whilst in 

 that of the pure water, the thermometer only rises to 45° or 47^0. 



The sowing being accompHshed, you will see in from 3 to 10 

 days, according to the species sown and the existing conditions, 

 yellow spots at the bottom of the vessel, and (if it be cylindrical, 

 specially at these points, produced by the caustics of refraction), 

 these grow rapidly from day to day. Soon the deposit occupies not 

 only the bottom of the vessel, but also its upright sides; while 

 bubbles of oxygen gas, released by the diatoms, rising incessantly, 

 carry upwards some of the newly-formed organisms, and produce a 

 mass on the surface of the liquid. If you cover vessels of any 

 considerable size, m this state, with a bell glass full of water, at the 

 end of fifteen days you may collect about 200 cms. of oxygen, 

 containing traces of pure hydrogen and of carburetted hydrogen, 

 probably resulting from the decomposition of the organic matters 

 of the maceration by means of bacterian ferments. 



There are other precautions on which it is useless to insist ; 

 the evaporated water should be replaced every ten or twenty days 

 by water sterilised at 70*^0. If the growth is to be continued the 

 liquid will be robbed of its mineral constituents, and some drops 

 of the before-mentioned solutions must be added — in this way 

 the multiphcation of the diatoms may be continued for two, three, 

 or even four months. I have to-day in my laboratory a growth 

 that, having been recharged two or three times, has been going on 

 since December 5th, 1891, and which has always been healthy. 



You may carry on in the same manner growths under the 

 microscope, the only difference being that they must be of less 

 volume — those which I use contain about 2 cms. of liquid. 



Such are the principal things necessary to be observed in order 

 to obtain, without difficulty, a growth of diatoms in fresh water. 

 Side by side with these normal growths, others may be produced 



