INFUSORIA. 
11 
thickly as they can lie, into patches. They constitute the 
genus Vibrio. Several may be seen among them briskly 
■wriggling along, which resemble a little coil of spiral wire. 
Such forms bear the generic appellation of Spirillum* 
As all infusions of vegetable or animal substances are 
found to be speedily filled with animals resembling these, 
in great variety, though not always of the same species, 
the circumstance has been seized by naturalists to afford 
a name by which this class of beings should be distin- 
guished. They have been therefore called Infusoria, or 
infusory animalcules ; a very extensive group, and one 
which, in a more advanced state of our knowledge, it may 
be found desirable to divide, since it includes animals of 
very different grades of organisation. Those of which we 
have spoken are among the simplest of those forms : we 
shall now describe others of a higher place in the scale, 
and more attractive in their appearance and in their 
habits. Every day during which the infusion is allowed 
to stand, it will display fresh forms, and generally those 
which appeared most abundantly in the earlier stages will 
be found successively to die out, and be replaced by other 
species. The more highly organised kinds will usually 
be discovered at the later periods. 
But there is a very beautiful form, and one which can- 
not fail to possess great interest for the young microscopi- 
cal student, which commonly occurs pretty early. Perhaps 
we shall sec some of the stalks of the macerated hay, or 
floating portions of the semi-decomposed leaves, clothed 
with what appears to the naked eye to be a very delicate 
* Recent researches, however, render it probable that these are the earliest 
stages of Intestinal Worms. 
