DISEASES OF CATTLE 127 



The sympathetic division consists of nerves and ganglia. The 

 muscular tissue, which acts independently of the will as, for ex- 

 ample, the stomach, intestines, womb, blood vessels, ducts, etc. is 

 called involuntary muscular tissue, and receives nervous stimulus 

 from the sympathetic division. 



The brain, spinal cord, and the ganglia are the central organs 

 of the nervous system. The nerves conduct the nervous influence. 

 The nerves terminate differently according to their function. The 

 terminations are called end organs. The terminal end organs in the 

 skin and other parts endowed with sensation receive the impressions, 

 which are conveyed to the brain, where they are appreciated. They 

 are so sensitive that the most gentle zephyr is perceived. They are 

 so abundant that the point of the finest needle can not pierce the 

 skin without coming in contact with them, and the sensation of pain 

 is instantly conveyed to the brain. The terminal end organs of the 

 nerves that supply the muscles are different, as they give the impulse 

 which is conveyed by the motor nerves to the elements which consti- 

 tute the muscle, and this impulse is the excitation which causes the 

 muscle to contract. The terminal end organs of the special senses of 

 taste, smell, etc., receive their special impressions, and their respec- 

 tive nerves carry the impressions to the brain. 



There are two divisions of nerves, the afferent and efferent. The 

 afferent nerves are those which convey the impression to the nerve 

 centers. All the sensory nerves belong to this division. The effer- 

 ent nerves are those which convey the nervous impulse outward from 

 the nerve centers, and they are further classified according to the 

 function of their respective centers. For example: Motor fibers 

 carry the impulse from the nerve center to a muscle to cause con- 

 traction. Vaso-motor fibers carry the impulse to the muscular tissue 

 in the blood vessels, which regulates their caliber. The secretory 

 fibers convey the impulse to the cells of the glands and excite the ac- 

 tivity of the gland, and its particular product is secreted or evolved, 

 as, for instance, milk in the mammary gland. Inhibitory fibers con- 

 trol or inhibit the action of the organ to which they are distributed, 

 as, for instance, the heart. 



Nerve centers may be considered as a collection or group of 

 nerve cells. Both the cerebro-spinal and the sympathetic divisions 

 have nerve centers. The centers derive their special names from 

 their functions. The brain is the great center of the nervous system, 

 as it is the center of intelligence and perception. The centers of all 

 the special senses, as well as the centers of various functions, are lo- 

 cated in different parts of the brain. Nerve centers also exist in the 

 spinal cord and in connection with the sympathetic system. 



A nerve is a cord consisting of a certain number of fibers of 

 nerve tissue, inclosed in a sheath of connective tissue. Nerves divide 

 and subdivide, sending off branches, which ramify in all parts of the 

 body, and, as they near their terminations, they contain but one or 

 two fibers. 



The brain and spinal cord are contained within a bony canal, 

 which forms a protective covering for them. The spinal cord, or 



