NERVOUS SYSTEM 39 



Sympathetic nerves. — These control, in part, involuntary 

 muscle fibers and through these the organs of circulation, respira- 

 tion, and digestion, the size of the pupil of the eye, and the 

 work of the various glands including the liver, spleen, pancreas, 

 and kidneys. 



Practical application. — Summarizing, we may say that the 

 cerebrospinal nervous system controls the muscles of the skeleton 

 (lean meat), gives sensation to skin and skeletal muscles, and 

 the special sensatioiLs of sight, hearing, taste, smell, etc. 



The sympathetic nervous system controls the involuntary 

 muscle fibers of the blood vessels, increasing or decreasing their 

 capacity as needed; it controls the involuntary muscle fibers of 

 the digestive organs, such as the stomach and intestines, produc- 

 ing the necessary motion automatically; it controls the move- 

 ments and work of the bladder, the movements of the hair, and 

 the involuntary muscle fibers of the iris (colored portion of the 

 eye) , making the pupil large or small, according to the intensity 

 of light. Directly or indirectly the sympathetic nerves also 

 control in part the work of secretion and excretion in the 

 salivary glands, liver, kidneys and other organs. 



The student should now make practical observations. He 

 may, for example, record past experience or present observations 

 concerning horses and cattle, taking those of sluggish, well 

 balanced, and highly nervous organizations. Compare these 

 different types as to working efficiency, feeding, and keeping. 

 Quiet steers do better. AVhat is the physiological explanation? 

 Note the effect of excitement on high type dairy cows as to 

 production — quantity and quality of milk considered. What is 

 the explanation? Wiiat connection between excitement in the 

 brain and milk in the udder? 



In making these studies, bear in mind that the quantity and 

 quality of digestive fluids, food absorption, distribution and 

 utilization of food material, the amount of blood flowing through 

 a cow's udder, and the degree of gland cell activity in the udder 

 are all under the direct influence of the nervous system. 



Disorders of the nervous system are often complicated and 

 difficult to handle. Veterinary services are usually necessary. 

 The following are typical disorders which the stockman should 

 understand in a general way. It is important to understand 

 that nerve tissue is subject to the same actual disease changes as 

 other tissues — atrophy, congestion, inflammation, and degenera- 



