56 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



explain one will doubtless be applicable to the other. Many 

 interesting facts have been established regarding ciliary move- 

 ments. The contractions of the cilia in any given field the 

 trachea, for instance follow in a definite sequence and are co- 

 ordinated. The waves of contraction progress in a definite direction. 

 This fact increases greatly the effectiveness of the cilia in per- 

 forming work. Thus, in spite of their extremely minute size, it 

 is estimated that an area of a square centimeter is capable of 

 moving a load of 336 gms. The contractions are automatic, 

 that is, the stimulus causing them is not dependent upon a con- 

 nection with the nervous system, but upon processes arising within 

 the cell itself; the cilia of a single completely isolated cell may 

 continue to contract vigorously. The movement may continue 

 for several days after the death of the individual, thus again showing 

 the physiological independence of the structure. The ciliated cells 

 may conduct a stimulus or impulse to other cells even after its 

 own cilia have lost their contractility. This fact is particularly 

 significant in general physiology, as it aids in showing that the 

 property of conductivity which is exhibited in such high degree 

 by nerve fibers is possessed to a lower degree by other tissues. 

 The ciliary movement is affected by variations in temperature, and 

 if the temperature passes beyond an optimum point the cilia fall 

 into a condition resembling heat rigor in the muscle. Their move- 

 ments are affected also by the reaction of the medium, being at 

 first accelerated and then slowed or destroyed by a slight degree 

 of acidity and favored by a very slight degree of alkalinity.* 



* References for physiology of ciliary movement: Verworn, "General 

 Physiology," English translation by Lee; Putter, "Ergebnisse der Physiol- 

 ogic," 1902, vol. ii, part n; Engelmann, article, "Gils vibratils," in Richet's 

 " Dictionnaire de Physiologic," vol. iii, 1898. 



