PREPARATION OF DIATOMS. 75 



and marine muds and to fossil deposits. In such are found Polycystins, 

 Radiolaria, Globigerina, Foraminifera, Sponges, Diatoms, and many other 

 infinitely small and very varied organisms. In the marine muds of 

 soundings only dead and mummified species are found. It is only at the 

 surface of seas and lakes that living examples exist, where both air 

 and light are abundant, and if in the deep muds a few specimens are 

 occasionally met with in good condition, it is only due to the fact that 

 they have dropped from the surface and that they have but lately 

 ceased to live. 



"A naturalist often experiences great difficulty in separating these 

 organisms from the pulverulent or crystalline mass {silicious, argillaceous 

 or calcareous), of which the greater portion of soundings consist. 

 These substances, often mixed for centuries with organic detritus form 

 usually a pasty or plastic mass, which may sometimes be even like 

 tar, and is very troublesome and difficult to separate. A large quantity 

 of volcanic ashes may also be frequently found mixed up with them. 

 Sometimes the sounding only consists of mineral material without any 

 trace of organisms. 



" In order to study organisms having silicious shells, e.g., Polycystins, 

 some Radiolaria, and especially Diatoms, it is indispensable to entirely 

 destroy this bulky organic matter. In guanos excrementary detritus are 

 abundant. They resist to an extraordinary degree the process of 

 putrefaction and even dissolvents, hydrochloric and nitric acid and 

 chlorine. All these organic detritus are equally incapable of being 

 levigated by reason of their varying specific gravity, and more particularly 

 because mineral particles so persistently adhere to them. 



"The following process effects the complete destruction of all this 

 organic matter, and as it does not give off any acid vapours it has the 

 advantage of not necessitating the use of a special laboratory or 

 a strong up draft current during cleaning. It also gives results superior 

 to any treatment with potassium chlorate or permanganate, or with 

 nitric acid, the chemicals usually employed, since all these give off acid 

 and corrosive vapours. 



"The desiccated mass (which may be pulverulent or compact) is treated 

 in a phial with diluted hydrochloric acid to remove the calcareous matter. 

 The phial should be sufficiently large to hold all the viscous scum which 

 the calcareous matter produces when it is thus intimately mixed up with 

 organic matter in a state of decomposition. When these salts have been 

 completely dissolved the liquid and the mud are placed on a filter paper, on 

 which the insoluble deposit is washed, and then dried on the same filter paper. 



