364 THE CULTIVATION OF DIATOMS 



Normal Cultures of Diatoms.— We have seen in the foregoing 

 three chapters the methods of carrying on these cultures, which 

 are those where the evolution of the Diatoms takes place in a 

 regular and natural manner, with the appearances that they present 

 in the media where they are commonly found. 



The utility of such cultures does not need to be shown ; 

 besides, the possibility of keeping at home at all seasons of the year 

 living Diatoms of the most varied kinds, the herbaria of diatomists 

 are by it remarkably simplified. Indeed, in his excursions, the 

 observer only needs to take sowings — the taking with him exten- 

 sive receptacles is often very useless, especially those ingenious 

 sacks or those grotesque knapsacks ; thirty little tubes, such as are 

 used for pilules — previously washed in boiling water, contained in 

 a box or portfolio, are, with pincers, all the necessary tools. 



Lastly, my comrade, the Surgeon-Major Couteand, sent in the 

 expedition of the Maiiche, conducted by the commandant Bee- 

 namie — an expedition which visited during last summer the 

 Shetland and Feroe Islands, Iceland, the island of Jan Mayen, 

 and Spitzbergen — has brought me 112 small tubes of various 

 deposits, both of fresh and sea water, taken from different places. 

 Many of these deposits could not be put in culture for fifty or 

 sixty days after they were collected. The result has surpassed my 

 expectations, and I have obtained by the methods that I have 

 described upwards of two hundred species of Diatoms, of which 

 I have made numerous preparations, to serve as a basis for a work 

 that ultimately I shall publish, with the help of my learned friend, 

 Dr. Couteand. Here is one of the first results of these processes 

 for the culture of Diatoms : — 



Abnormal Culture of Diatoms.— I have given this name to 

 cultures where the nutrition is slightly or largely modified, whether 

 by means of chemical elements or by physical agents, favouring, 

 as the case may be, either the development or the suppression of 

 the diatomic life. 



The anomaly may be dependent on physical agents. Indeed, 

 Diatoms raised under artificial light may, according to their nature, 

 give very fine or very poor results. Many of these algae accommo- 

 date themselves very well to a feeble light (a jet of gas burning 

 from fifty to sixty litres per hour) ; of this number many Nitzschias, 



