618 Cerebral Hyperemia. 



3. Cerebral Hyperemia. 



A number of diseased conditions have been ascribed, especiall}^ by- 

 old authors, to hyperemia of the brain, which were due either to 

 diseases of the brain that were not recognizable to the naked eye, or to 

 disease of other organs. Marked congestion of the vessels of the l)rain 

 and the membranes were held to be sufficient to explain the symptoms. 

 It must be remembered, however, that such congestion may be due to 

 the head being in a position lower than the body either at the time of 

 death or after, and experiments by Johne, Kitt and Dexler have shown 

 that there may be pronounced congestion of these vessels in healthy 

 animals or animals that have died from other diseases. The older ob- 

 servations cannot therefore be taken as accurate, and it remains un- 

 decided to what extent these postmortem alterations were taken into ac- 

 count by the old authors. In the vast majority of cases, the diagnosis 

 was based simply upon clinical symptoms or upon references to the 

 subject in the older literature. Examination of the causes mentioned, 

 shows that the nervous symptoms Avould be of (juite a different kind, 

 and that in many cases not only would there be no hyperemia, but an 

 actual anemia. 



It cannot be doubted that variations occur in the amount of arterial 

 blood in the brain ; but, as rightly pointed out by Dexler, and as ob- 

 served in the human subject, these variations are manifested more by 

 subjective than objective symptoms. The recognition and correct in- 

 terpretation of these symptoms is associated with great difficulty. It 

 is certainly rare to find deep-seated disease of the brain unassociated 

 wuth active hyperemia, which is recognizable clinically, and at the post- 

 mortem. 



Etiology. The following are some of the influences which 

 may determine an increased flow of blood to the arteries of the 

 brain: increased cardiac activity, loss of tone of the cerebral 

 arteries, overexertion, rough handling during the process of 

 breaking-in, severe psychical disturbances during transport by 

 train or boat, rutting, fear, hypertrophy of the heart, acute 

 poisoning with alcohol and other narcotics, direct rays of the 

 sun falling on the head, too great heat, etc. A kind of collateral 

 hyperemia is set up wdien large areas are cut off from a supply 

 of arterial blood as in thrombosis of the posterior aorta or other 

 large vessel, and when the abdominal vessels are compressed 

 owing to t^anpanites. Acute inflammatory processes of the brain 

 and membranes are always associated with hyperemia, but such 

 instances are more conveniently considered in connection with 

 the causal condition. 



Passive congestion may be caused by compression of the 

 jugular veins by the splehius muscle, tumors, enlarged thyroids, 

 and any sort of inflammatory swelling. It may also be set up 

 by a weak heart, chronic lung disease, or compression of the 

 lungs owing to gastric or intestinal tjniipanites. 



Anatomical Changes. In case of acute hyperemia of the 

 brain and membranes the brain substance is reddish or yellow 



