112 DISEASES OF CATTLE. 



trol of the will. For example, the voluntary muscular tissue includes 

 all the muscles which act as the will directs. Another example, if 

 anything comes in contact with any part of the skin, the impression is 

 immediately perceived. All the special senses belong to this division. 



The sympathetic division consists of nerves and ganglia. The muscu- 

 lar tissue which acts independently of the will, as, for example, the 

 stomach, intestines, womb, blood-vessels, ducts, etc., is called involun- 

 tary muscular tissue, and receives nervous stimulus from the sympa- 

 thetic 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 constitute 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 respect- 

 ive impressions, and their respective nerves carry the impressions to 

 the brain. 



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



The efferent nerves are those which convey the nervous impulse out- 

 ward 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 contrac- 

 tion. 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 activity of 

 the gland, and its particular product is secreted or evolved, as for in- 

 stance, milk in the mammary gland. Inhibitory fibers control or inhibit 

 the action of the organ to which they are distributed, as, for instance, 

 the heart. 



The afferent nerves are those which convey the impulse to the nerve 

 centers. All the sensory nerves belong to this division. 



Nerve centers may be considered as a collection or group of nerve 

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

 centers. The centers derive their special names from their functions. 

 The brain, as a matter of course, is the great center of the nervous sys- 

 tem, 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 

 located" in different parts of the brain. Nerve centers also exist in the 



