GENERAL PHYSIOLOGY OF MUSCLE-TISSUE 89 



determined. It will then be seen that the movement is, as a rule, alter- 

 nately a backward and a forward one, the cilium lowering and then rais- 

 ing itself, the latter taking place more quickly and energetically than the 

 former. As the cilium raises itself it becomes somewhat flexed in a direc- 

 tion corresponding to that of the general movement. The movement, 

 however, varies in character in different situations and in different animals. 

 The cause of the movements and the mechanism of their coordination are 

 unknown. They are, as far as known, independent of the nerve system. 

 The force of ciliary motion is very great. A load of twenty grams can be 

 supported and carried forward by the cilia on the mucous membrane of the 

 mouth and esophagus of the frog. The activity of the cilia is associated with 

 the nutrition of the cell of which they are a part and rises and falls with it. 

 Experimentally it has been found that the rate and energy of the movement 

 are greatest at a temperature of about 35 to 4OC., especially if they are 

 bathed with normal saline, rendered slightly alkaline. Low temperatures, 

 acids, alkalies, carbon dioxid, etc., retard the movement. 



The function of the cilia, though not always apparent, is associated with 

 the function of the passages in which they are found. As the surfaces of 

 these passages are swept by a current of considerable power, it is probable 

 that they assist in the passage of the materials which ordinarily traverse 

 them. Mucus and particles of dust are carried upward through the air- 

 passages; the ovarian cell is carried from the ovary toward the uterus; the 

 spermatozoa, as well as the fluid in which they are contained, are carried 

 forward through the epididymis ducts. 



