532 MUSCLE-NERVE PHYSIOLOGY 



nodes of contraction of the muscle, figure 333, B. The whole fiber is thick- 

 ened at the contraction nodes and stains very readily and usually uniformly. 

 However, by certain stains the fibrillae can be traced through the node. The 

 node is an apparent area of chemical differentiation. There is a marked con- 

 densation of the intermuscular fibrous tissue, which is doubtless purely a 

 passive phenomenon. The most striking change during contractions is 

 observed in the nucleus, figure 333, A, and figure 334. The nucleus during 

 rest is a long slender oval or spindle with a general chromatic network. 

 1 'During contraction, the smooth muscle nuclei shorten and thicken by an 

 active process. The chromatin collects, chiefly at the two ends of the nu- 

 cleus, leaving a relatively clear area in the center." 



Ciliary Motion. Ciliary motion, which is closely allied to ameboid 

 and muscular motion, is alike independent of the will, of the direct influ- 

 ence of the nervous system, and of muscular contraction. It may continue 

 for several hours after death, or removal of the ciliated tissue, provided the 

 portion of tissue under examination be kept moist. Its independence of the 

 nervous system is shown also in its occurrence in the lowest invertebrate 

 animals which are apparently unprovided with anything analogous to a 

 nervous system, and in its persistence when the ciliated cells are completely 

 separated from each other by teasing out in serum or other physiological 

 solution. The vapor of chloroform arrests the motion; but it is renewed 

 on the discontinuance of the application of the anesthetic. The movement 

 ceases when the cilia are deprived of oxygen (although it may continue for 

 a time in the absence of free oxygen), but is revived on the admission of this 

 gas. Carbon dioxide also stops the movement. The contact of various 

 substances, e.g., bile, strong acids, and alkalies, will stop the motion alto- 

 gether; but this depends chiefly on destruction of the delicate substance of 

 which the cilia are composed. Temperatures above 45 C. and below o C. 

 stop the movement, whereas, moderate heat and faintly alkaline solutions 

 are favorable to the action and revive the movement after temporary cessation. 

 The exact explanation of ciliary movement is not known. Whatever may 

 be the exact explanation, the movement must depend upon some changes 

 going on in the cells of which the cilia are a part and not on changes limited 

 to the cilia themselves, since, when the latter are cut off from the cell the 

 movement ceases, and when severed so that portions of the cilia are left 

 attached to the cell, the attached and not the severed portions continue the 

 movement. Ciliary contraction is to be regarded as a type of motor activity 

 carried out in a specialized form of motor apparatus. The changes going 

 on in the cell must be classed with similar changes in heart or skeletal 

 muscle. Ciliary tissue is like cardiac in at least two characteristics: the cells 

 are capable of conducting a stimulus from cell to cell, and ciliary activity 

 is automatic. As a special illustration of cilia-like action may be mentioned 

 the motion of spermatozoa, which are cells with a single cilium. 



