594 VETERINARY PHYSIOLOGY 



any marked physiological effect or to account for the tone of the 

 arterioles. An amount sufficient to act upon them causes 

 marked paralysis of the gut. It is to be regarded as a reserve 

 stimulant which is called upou when the true sympathetic 

 system is powerfully stimulated, as it is in various disturbances 

 of the central nervous system which are accompanied by such 

 emotional conditions as fright or anger. The stimulation of 

 the true sympathetics leads to the increased action of the 

 heart and the contraction of the abdominal vessels with the 

 increased flow of blood to the muscles, and to the other 

 physical accompaniments of the emotions which are preparations 

 for meeting the conditions producing them. If the stimulus is 

 sufficiently powerful, the effect is augmented and sustained 

 by an outpouring of adrenalin. 



5. Detection of Adrenalin in the Blood. — The most delicate 

 method for testing the amount of adrenalin is the inhibitory 

 action upon a strip of intestine in oxygenated Ringer's solution 

 at the body temperature. This action is manifested by as little 

 as 1 in 400 million. 



6. Toxic Action. — The administration of large doses of 

 adrenalin may cause death from pulmonary congestion. Re- 

 peated doses result in degenerative changes in the liver, and 

 in a thickening of the inner coat of the arteries. 



2. Hypophysis Cerebri. 



1. Development. — Tliis is formed as a hollow downgrowth 

 from the base of the third ventricle of the brain. In some 

 animals the stalk remains open, but in man it is closed 

 (fig. 230). 



2. Structure. — It forms what is anatomically the posterior 

 lobe of the pituitary body lying in the sella turcica. It is com- 

 posed of neuroglia cells, but in it are frequently found little 

 masses of colloid and cells resembling those of the inter- 

 mediate part of the pituitary (p. 599) a structure which closely 

 embraces the hypophysis. 



' 3. Physiology. — (a) Removal produces no marked symptoms. 

 (b) Extracts, when injected into a vein cause — 

 (1) A rise of blood pressure from constriction of the 



arterioles. If the dose be repeated within half an hour, this 



