GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 101 



far as the pulmonary lobules/frallopjan tubes, uterus, and epididymis. 

 The lumen of the central canal oTtTie "spinal cord and the cavities of 

 the brain are lined, especially in childhood, by cells provided with 

 similar cilia<^Ciliated epithelium is also found in all classes of ani- 

 mals, and especially 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 trans- 

 parent 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^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 rapidity 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 raising itself, the 

 latter taking place more quickly and ener- 

 getically than the former. As the cilium 

 raises itself it becomes somewhat flexed in 

 a direction corresponding to that of the 

 general movement. The movement, how- F IG . 42 _ CILIATED EPI- 

 ever, varies in character in different situa- THELIUM. 



tions 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 nervous 

 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 40 C., especially if they 

 are bathed with normal saline, rendered slightly alkaline. Low 

 temperatures, acids, alkalies, carbon dioxid, etc., retard the move- 

 ment. 



The function of the cilia, though not always apparent, is asso- 

 ciated 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 



