248 PHYSIOLOGY 



In order that the central nervous system should have efficient control over 

 such a tissue, it must be able to influence it in two directions : it must be 

 able to induce a contraction or increase a contraction already present, and 

 it must also be able to put an end to a spontaneous contraction, i.e. to induce 

 relaxation. In order to carry out these two effects, smooth muscle receives 

 nerve fibres of two kinds from the central nervous system, one kind motor, 

 analogous to the motor nerves of skeletal muscle, the other kind inhibitory, 

 causing relaxation or cessation of a previous contraction. All these fibres 

 belong to the visceral or ' autonomic ' system. They are connected with 

 ganglion-cells in their course outside the central nervous system, and their 

 ultimate ramifications in the muscle are always non-medullated. A typical 

 tracing of the opposite effects of these two sets of nerves is given in Fig. 97. 



In the invertebrata many ' voluntary ' striated 

 muscles probably possess a double innervation. 

 Thus in the crayfish the adductor muscle of the claw 

 consists of striated muscular fibres, every fibre of 

 which is supplied with two kinds of nerve fibres. 

 By exciting these fibres one may get, according to 

 the conditions of the experiment, either contraction 

 of a relaxed muscle or relaxation of a tonically con- 

 j f J t t j 4 _ t tracted muscle (Fig. 98). 



FIG 98 Tracing of contraction AMCEBOID MOVEMENT 



of adductor muscle of claw of 



crayfish, showing inhibition re- Amoeboid movement is seen in the uni- 

 sulting from stimulation of its ,, , . , ,, -, 



nerve (at 6) by means of a con- cellular organisms such as the amoeba and 



stant current. The break of the m the white blood corpuscles. It Can OCCUr 

 current^ causes a second smaller , .., . , . ,. ., ,. . 



inhibition. (BIEDERMANN.) only within certain limits of temperature 



(about 0C. to 40) ; within these limits it is 



the more active the higher the temperature. At about 45 the cell goes 

 into a condition resembling heat rigor. 



The fluid in which the corpuscles are suspended is of great importance. 

 Distilled water, almost all salts, acids and alkalies, if strong enough, stop the 

 action and kill the cell. 



The movements are also stopped by C0 2 or by absence of oxygen. 

 Artificial excitation, whether electrical, chemical, or thermal, causes 

 universal contraction of the corpuscle, which therefore assumes the spherical 

 form. 



CILIARY MOVEMENT 



Cilia are met with in man in nearly the whole of the respiratory 

 passages and the cavities opening into them, in the generative organs, in the 

 uterus and Fallopian tubes of the female, and the epididymis of the male, and 

 on the ependyma of the central canal of the spinal cord and its continuation 

 into the cerebral ventricles. 



The cilia (Fig. 99) are delicate tapering filaments which project from the 

 hyaline border of the epithelial cells. There are about twenty or thirty to 

 each cell. The hyaline border is really made up of the enlarged basal portions 

 of the cilia. 



