INFUSORIA. 77 
The spiral or helicoidal form of the chains is not easily perceived, unless the chains are 
thrown on edge, (as in fig. 42, b.) This is easily effected with Chevalier’s compressor. 
Alcohol completely dissolves the endochrome of this species, and the solution, when evapo¬ 
rated, leaves a greenish resinous mass. The frustules, after the action of alcohol, are as 
colorless as glass, and resist the action of fire and nitric acid. 
The infusoria are so minute, that many millions of their shells and coverings are contained 
in a cubic inch of the infusorial earth, which forms extensive deposits in many parts of our 
country, and particularly in the primary regions of New-England and New-York. By the 
silent, and until lately unnoticed operations of such minute animals, the foundations of new 
surfaces, capable of subsequent tillage, are laid. Daily additions are thus made to the habita¬ 
ble surface of the earth, and the stagnant ponds and marshes become verdant and beautiful 
meadows. These minute animals undoubtedly secrete the siliceous matter from the silex 
dissolved in the water in which they live, as we do the materials in our bony system from 
the food that we eat. 
The primary rocks, by their gradual decomposition, yield silex in solution by the aid of 
jDotassa, which combines with it in the nascent state; and thus these animals are probably 
in part provided with the means of secreting it so as to form their coverings, and give rise to 
there being a greater proportion of this infusorial earth in such countries, than where the 
rocks are composed of the disintegrated and recomposed fragments of preexisting ones; as 
we see in the case of lake marl, which abounds most in limestone regions, or where the 
springs or decomposing rocks furnish the greatest quantity of carbonate of lime in solution, 
from which the molluscous animals secrete it. 
Lime, whence derived. 
Several authors, among whom are Thomson, Macculloch, Bakewell and others, have 
revived the idea that lime has been formed from organic secretion, and that the vital powers 
have combined elements to form them. This idea is carried out by many to so great an 
extent, as to suppose the greater abundance of calcareous rocks in the more recent than in the 
older rocks, was caused by the quantity continually formed by succeeding races of animals for 
their own use, being greater than was necessary to supply the next succeeding race, so that 
a surplus was continually accumulating. There are no facts to justify such a theory, which 
can not be explained on other grounds, and a multitude of facts militate against it. 
It is a matter of common notoriety, that shells do not abound in ponds or lakes where there 
are no limestone rocks, calcareous springs, or springs of hard water. Almost all soils contain 
a little carbonate or muriate of lime, some of which is carried by the surface and spring 
waters in a state of solution into the marshes, brooks and ponds. It there serves as a cover¬ 
ing to the testacea, when secreted by them, as the animal system secretes the various sub¬ 
stances necessary for itself from its food. But in soils that furnish little carbonate or muriate 
of lime, the testacea do not accumulate, because each succeeding race consumes the shells 
