

GENERAL ANATOMY OF THE EPITHELIUMS. 189 



those of the pharynx in the frog), by their contact cause 

 those next to them to enter into action ; and thus, by the 

 mechanism of constantly succeeding impulses, this wonderful 

 chain of influences is produced. 



If, however, the cilia be detached from the cell to which 

 they belong, they immediately cease to move : their life is, 

 thus, evidently bound up with that of the cell, and especially 

 of the protoplasm filling the cell of which they form a part ; 

 Eberth and Marchi, indeed, have discovered that, in the 

 mollusks, the vibratory cilia penetrate the plane with which 

 the free base of the cell is furnished, and come in close con- 

 tact with the cellular contents ; and, by means of the modi- 

 fications which the vibratile cilia undergo at the beginning 

 of a coryza, Ranvier has shown that this important feature 

 of structure is found in man also. 



Different circumstances tend to modify the vibratile 

 movements of these epitheliums: they have been studied 

 with great minuteness by Michael Forster and by Calli- 

 burces in the oesophagus of the frog. They are checked 

 by anesthetics (ether, chloroform), but regain their vi- 

 vacity on withdrawal of the vapor; according to Michael 

 Forster, the absence of oxygen appears to paralyze them 

 as if by producing a state of asphyxia. Acids render them 

 immovable, but alter their structure; the movements may, 

 however, be resumed, if the acid be much diluted and neu- 

 tralized by an alkaline solution ; these alkaline solutions are 

 very effectual in accelerating the motion (acids and alkalies 

 produce an exactly similar effect upon the sperm utozoids). 

 A low temperature Blackens their motion, whilst a high one 

 increases it ; in the hibernating animals the movements ap- 

 pear to cease during hibernation (?). No poison has any 

 effect upon them, unless the animal be poisoned, or the poi- 

 sonous substance placed directly on the epithelial surface. 1 



1 A curious fact has been brought to the notice of the Ameri- 

 can editor. The American black bear, which is a good illustra- 

 tion of a hibernating animal, cannot eat food in winter with 

 impunity. Two bears were kept during one winter under obser- 

 vation. As in their natural abode they went to sleep on the first 

 appearance of cold weather. Two or three times they were easily 

 aroused from their sleep, and during one of these occasions one of 

 them was induced to take a very small portion of simple food. 

 During the next two or three days, though asleep most of the time, 

 it sickened and died. The other bear, who was not allowed to be 

 disturbed until the opening of spring, recovered his activity; but, 



