78 (14 2 ) Society for Experimental Biology and Medicine. 



These experiments have been repeated for the purpose of making 

 detailed histological studies and in the hope of throwing some light 

 upon the histogenesis of arteriosclerosis in man. 



Methods. — Rabbits have received injections of a I to 1,000 

 solution of adrenalin in the ear vein. An initial dose of 3 m. re- 

 peated every other day has been the usual procedure. In other 

 instances, the dose has been gradually raised until a dose of 20 m. 

 to 25 m. was given every day. The animals have been killed 

 after periods varying from a few days to eight weeks. 



Results. — The vascular lesions produced are limited to the 

 aorta and exhibit a more or less definite sequence. Rabbits re- 

 ceiving five to six injections show no gross lesions, but histologic- 

 ally important changes in the media are evident. These consist 

 of focal areas of degeneration in which the muscle fibers are de- 

 stroyed without alteration of the elastica. Later the degeneration 

 is more extensive and involves the greater portion of the middle 

 zone of the media. At this time changes in the elastic tissue ap- 

 pear ; the fibers become swollen, stain irregularly and in some 

 places appear to be fused together. Special stains show a small 

 number of minute fat droplets in such areas. After twelve to 

 fifteen injections very definite lesions are evident macroscopically. 

 The aorta is more or less distorted, rigid and nonelastic. Irregular 

 dilations alternate with elevated brittle areas of calcification. Dis- 

 tinct atheroma with ulceration is seldom seen. In the experiments 

 continued for six to eight weeks, the process becomes very diffuse 

 and small dilations of the thinner portions of the aorta assume the 

 appearance of aneurysms. At this stage the destruction of the 

 elastic fibers is extreme and all degenerated areas are infiltrated 

 with lime salts. Cellular infiltration and repair about such areas 

 have been seen in a few instances, and experiments are now under 

 way to determine the frequency and extent of this reparative 

 process. 



The changes in other organs include enlargement of the heart, 

 edema and congestion of the lungs, also degenerative changes in 

 the liver and kidney, and occasionally in the heart and other 

 muscles. 



Whether the vascular changes are due to a primary toxic action 

 of the adrenalin or whether they arc the result of the increased 



