108 GENEEAL BISTOEY OF THE INFUSOEIA. 



is siiecessMly adopted by Prof. Bailey and D'Orbigny, and is thus described 

 by the former {Proceedings of AmeAcan Assoc, for the Advancement of Science, 

 1849, p. 409) : — " A\Tiere the mixtiu-e of inorganic matter is in large propor- 

 tion to the Infusoria and other microscopic organisms, and corresponds nearly 

 in specific gravity," the deposit is to be thoroughly dried, whereby the minute 

 unbroken shells wiR become filled with air, and consequently when rapidly 

 stirred up with water they will be buoyed up, and continue suspended after 

 the intermixed sand has settled at the bottom. They may then be easily re- 

 moved from the suiface and transferred by alternately touching the surface 

 of the water with the finger, and the glass slide on which they are to be placed. 

 The sediment, if diied again, will often yield another abundant supply of the 

 minute shells. " By the above means," adds Dr. Bailey, " I have obtained 

 exquisite specimens from the bottom of diied-up ponds, fi'om the sands of 

 harbours, and from the mud attached to floating ice in the Hudson Eiver, — 

 materials presenting the two extremes of very coarse gravel and the finest 

 sediment, neither of which would have given good residts by any other 

 process." 



In the case of some deposits the shells of the Diatomaceae are so far the 

 chief constituents, that no preparation is needed before subjecting them to 

 microscopic investigation. 



The cohesion of Diatomaceous deposits is at times so great that a difficulty 

 is encountered in separating them. A method of dealing with such is de- 

 tailed by Prof. Bailey (Sill. Journ. 1856, p. 356) : — " Many masses of fossil 

 Diatomaceae are so strongly coherent, that they cannot be diff'used in water 

 (for the purpose of mounting in balsam) without a degree of mechanical vio- 

 lence which reduces to fragments many of the most beautiful and interesting 

 forms. This is particularly the case with some specimens from the ' infusorial 

 deposits ' of Cahfornia. Some of these I endeavoured to break up by boiling 

 in water and in acids, and also by repeated freezing and thawing when moist- 

 ened, but without good results in either case. At last it occuiTcd to me that 

 the adherence might be due to a slight portion of a silicious cement, which 

 the cautious use of an alkaline solution might remove without destrojdng any 

 but the most minute shells of the Diatoms. As the case appeared a desperate 

 one, a ' heroic remedy ' was applied, which was, to boil small lumps of the 

 Diatomaceous mass in a strong solution of caustic potassa or soda. This proved 

 to be perfectly efficacious, as the masses under this treatment rapidly split up 

 along the planes of lamination and then crumbled to mud, which, being im- 

 mediately poured into a large quantity of water, ceased to be acted upon by 

 the alkali, and gave, when thoroughly washed, not only all the large shells 

 of the Diatoms in a state of unhoped-for perfection, but also furnished abun- 

 dance of the minute forms. Having obtained by this method highly satis- 

 factory results from specimens from many localities, I can confidently recom- 

 mend it as an addition to oiu' modes of research. 



" The following directions wiU enable any one to apply the process : — Put 

 small lumps of the mass to be examined into a test tube, with enough of a 

 solution of caustic potassa or soda to cover them ; then boil over a spuit-lamp 

 for a few seconds, or a few minutes, as the case may require. If the solution 

 is sufficiently strong, the masses wall rapidly crumble to mud, which must be 

 poured at once into a large quantity of water, which, after subsidence, is re- 

 moved by decantation. If the mass resists the action of the alkaHne liquor, 

 a still stronger solution should be tried, as, while some specimens break up 

 instantly in a weak solution of alkali, others require that it should be of the 

 consistence of a dense sjTTup. The mud also should be poured ofi" as fast as 

 it forms, so as to remain as short a time as possible in the caustic ley. 



" The only specimens which I have found not to give good results by the 



