156 



Prof. Ehrenherg on Fossil Infusoria. 



[Jan. 



ly o{ Navicula viridis ^ the mass from the Isle of France Bacillaria 

 vulgaris; that of ^miY'iox^ Synedra capitata ; and that of Bilin is 

 so entirel}^ formed of Gaillonella distans that the other species of ani- 

 malcules are only scattered through it. 



Finally, the proportion of these animals merits a passing attention. 

 The millions of the tribe of infusoria have often been mentioned, and 

 spoken of almost without consideration of their number, perhaps be- 

 cause little belief is entertained of their corporeality. They have often 

 been regarded as drops of oil and appearances of various kinds ; but since 

 the Polirschiefer of Bilin must be acknowledged to consist almost en- 

 tirely of an aggregation of infusoria in layers, without any connecting 

 medium, these infusoria begin to acquire a greater importance, not 

 only for science, but for mankind at large. The Kieselguhrs occur, 

 it is said, only in nests about the size of a fist or a head, and probably 

 may be of comparatively recent origin. With the Polirschiefer it is 

 different ; this forms widely extended layerSj containing fossil plants 

 and fishes. A single druggist's shop in Berlin consumes yearly more 

 than 20 cwt. : the consumption therefore of infusoria as tripoli and for 

 casting-moulds in Berlin and the environs may be perhaps estimated 

 at 50 to 60 cwt, yearly, and thence we may in some measure infer the 

 sale in Bilin. I hope to receive in a short time more extensive details 

 on this subject : it is sufficient at present to say, that the infusoria 

 supply all the requisite demands for purposes of practical utility. 

 Passing over the share they have in the Raseneisen, the soldier cleans 

 his arms with tripoli ; the worker in metal, the locksmith and the en= 

 graver polish with infusoria, which serve also for moulds in founderies. 

 These animals which are so useful after death, and form entire rocks, 

 have at present a more special interest in their individuality. The size 

 of a single one of these infusoria, which form the Polirschiefer, 

 amounts upon an average and in the greater part to -g-i^ of a line, 

 which equals i- of the thickness of a human hair, reckoning its average 

 size at ^'g- of a line. The globule of the human blood, considered at 

 ■jiof not much smaller. The blood globules of a frog are twice as 

 large as one of these animalcules. As the Polirschiefer of Bilin is 

 slaty, but without cavities, these animalcules lie closely compressed. 

 In round numbers, about twenty-three millions of animals would make 

 up a cubic line, and would in fact be contained in it. There are 17'^S 

 cubic lines in a cubic inch, and therefore a cubic inch would contain on 

 an average about 41,000 millions of these animals. On weighing a 

 Cubic inch of this mass, I found it to be about 220 grains. Of the 41,000 



