468 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 fibrillse 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. 

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

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

 nucleus, 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 altogether; 

 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 spe- 

 cialized 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. 



