40 LECTURE III. 



Danish observer of Infusoria, only succeeded in reviving them when 

 they were surrounded by foreign particles, and defended from the 

 air. Both Oken and Rudolphi deny the revival of desiccated 

 animals ; but later observers have succeeded in producing the won- 

 derful phenomena described by Spallanzani, especially Professor 

 Schultze ; and I myself witnessed at Freiburg, in 1838, the revival of 

 an Arctiscon which had been preserved in dry sand by the Professor 

 upwards of four years. 



I have already, at the close of the previous lecture, alluded to the 

 important functions, apparently so disproportionate to their size and 

 powers, which the Polygastria perform in relation to the conservation 

 of organic matter and of the purity of the atmosphere. They like- 

 wise take their share in modifying the crust of the earth. It has 

 been shown that some Polygastria are naked, others loricated or 

 defended by silicious shells, of definite and easily recognisable forms 

 and patterns in different species. Prof. Ehrenberg had not long made 

 these observations before he discovered that a certain kind of sili- 

 cious stone, called Tripoli or Polierschiefer, was entirely composed 

 of such cases; was in fact the debris of Polygastric Animalcules, 

 chiefly of an extinct species, called Gaillonella distans. The sub- 

 stance alluded to has long been well known in the arts, being used in 

 the form of powder for polishing stones and metals. At Bilin, in 

 Bohemia, there is a single stratum of this substance, not less than 

 fourteen feet thick, forming the upper layer of a Tripoli hill, in every 

 cubic inch of which layer Ehrenberg estimates that there are forty- 

 one thousand millions of individuals of the Gaillonella distans. It 

 likewise contains the shells of NaviculcE, Bacillaria^ ActiJiocyclus, 

 and other silicious animalcules. The lower part of the stratum con- 

 sists of the skeletons of these animalcules, united together without 

 any visible cement ; in the upper and more compact masses the in- 

 fusory shells are cemented together, and filled by amorphous silicious 

 matter, formed out of dissolved cases. Corresponding deposits of 

 the silicious cases of these animalcules have since been discovered in 

 many other parts of the world, some including fresh water, others 

 marine species of Infusoria. A quantity of a pulverulent matter is 

 deposited upon the shores of the lake near Uranea in Sweden, and 

 which from its extreme fineness resembles flour. This has long been 

 known to the poorer inhabitants under the name of Berg-mehl, or 

 mountain meal, and is used by them mixed up with flour as an article 

 of food : it consists almost entirely of the silicious shells of pulverised 

 Polygastria. Most of the infusorial formations, as the polishing slates 

 of Cassel, Planitz, and Bilin, are, in fact, extraordinary monuments, 

 which have handed down to us the record of the existence of Poly- 



