GENERAL PHYSIOLOGY OF MUSCLE-TISSUE 89 



Eustachian tube, larynx, with the exception of the vocal membranes, trachea 

 and bronchial tubes as far as the pulmonary lobules, Fallopian tubes, uterus, 

 and epididymis. The lumen of the central canal of the spinal cord and the 

 cavities of the brain are lined, especially in childhood, 

 by cells provided with similar cilia. Ciliated epithe- 

 lium is also found in all classes of animals, and espe 

 daily in the invertebrates. 



The cilia found in the human body vary in length 

 from 0.003 mm. to 0.005 mm - They are apparently 

 structureless and colorless, and appear to have their 

 origin in and to be a prolongation of a transparent 

 material on the outer surface of the cell material. The 

 number of cilia present on the surface of any individual 

 cell varies approximately from five to twenty-five. FlG ' 

 When ciliated epithelial cells, freshly removed from 

 the mucous membrane and moistened with normal saline, are examined 

 with the microscope, it will be found that the cilia are in continuous and 

 rapid vibratile movement, so much so that the individual cilium cannot 

 be distinguished. In time, however, their vitality declines and the rapid- 

 ity of movement diminishes. When the movement of the individual 

 cilium falls to about eight or ten per second, its character can be readily 

 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. 



