68 INFUSORIA. PART m. 



amount of germs no larger than the 2 4^ooo^ n or 



part of an inch in diameter; and since according to 

 MM. Snllivant and Wormley, vision with the most 

 powerful microscope is limited to objects of about the 

 smooth part of an inch in diameter, we need not be sur- 

 prised if Infusoria and other organisms appear in pu- 

 trescible liquids in far greater numbers than the germs 

 in atmospheric dust visible by the aid of microscopes 

 would lead us to expect. 



The ferments are the least in size and lowest in or- 

 ganization of all the Infusoria. The higher group 

 which abounds in stagnant pools and ditches are ex- 

 ceedingly numerous, and their forms are varied beyond 

 description. They are globular, ovoid, long and slender, 

 short and thick, many have tails, one species is exactly 

 like a swan with a long bending neck, but whatever 

 the form may be, all have a mouth and gullet. 

 Although the skin of the Infusoria is generally a mere 

 pellicle, that of the red Paramcecium and some others 

 resembles the cellulose covering of a vegetable cell, 

 engraved with a pattern ; but in all cases respiration is 

 performed through the skin. 



, Whatever form the cell which constitutes the body 

 of the Infusoria may have, the highly contractile dia- 

 phanous pellicle on its exterior is drawn out into minute 

 slender cilia which are the locomotive organs of these 

 creatures. Yibrating cilia form a circlet round the mouth 

 of some of these animalcules, a group of very long ones 

 are placed like whiskers on each side of it, as in the 

 Paramcecium caudatum, and in some cases there is a 

 bunch of bristles in front. Certain Infusoria have 

 cilia in longitudinal rows, and in many the whole body 

 is either partially or entirely covered with short ones. 

 In some Infusoria their vibrations are constant, in 

 others interrupted, and so rapid that the cilia are in- 

 visible. These delicate fibres which vary from the 



