Symptoms. Course. Diayiiosis. 619 



in color, the venous plexuses of the pia are deep red and there 

 may be echynioses. The lesion described may often be missed 

 in spite of there having been active hyperemia during life,Jje- 

 cause it tends to disappear for the most part after death (Kitt, 

 Dexler). 



In passive hyperemia there may be ol)served a pronounced 

 congestion even in the small vessels and the tortuous course of 

 the veins may be traced on the surface of the brain, between the 

 convolutions, and even into the cortex. Small hemorrhages 

 may be found along the course of the vessels, an increase m the 

 otherwise clear cerebrospinal fluid and a saturation of the tis- 

 sues with serum. 



Symptoms. In cases of active hyperemia the period of ex- 

 citement may be followed by one of depression with repeated 

 recurrences of excitement. In slight cases the animals are rest- 

 less and excited, the eyes are bright, the pupils dilated, and the 

 pulse and respiration accelerated. The cranium feels abnor- 

 mally hot and the mucous membranes of the head are injected. 

 There appears to be some disturbance of consciousness as is in- 

 dicated by awkwardness of movement, alarm, and loss of 



appetite. . n i i 



Passive hyperemia is generally characterized by depression, 

 cyanosis of the mucous membranes, difficulty of respiration, and 

 a small rapid pulse. It-must be remembered that the brain pos- 

 sesses great adaptability to slowly progressive circulatory dis- 

 turbances, and consequently symptoms are usually absent m 

 cases of severe but long-standing congestion. 



Course. Simple arterial hyperemia generally passes off 

 within a few hours. In favorable cases the condition returns 

 to the normal either suddenly or gradually, and within a fey 

 hours all symptoms may have disappeared. Venous hyperemia 

 is a temporary condition in cases in which the cause of the con- 

 gestion can be removed. In other cases it is persistent, increas- 

 ing from time to time, and may lead to the production of great 

 depression. 



Diagnosis. In slight cases the normal condition of the ani- 

 mal, as regards its cerebral functions, its age and strength, must 

 be considered. The periodic appearance of sexual impulse must 

 be taken into consideration, for this sometimes causes similar 

 changes in animals. The possibility must not l)e lost sight ot 

 that the svmptoms of hyperemia mark the onset of some acute 

 infectious' disease, or that some organic disease of the bram, 

 stomach or intestine may be behind it. Diagnosis and prognosis 

 in the early stages must be made, taking into consideration the 

 possible development of further symptoms. As a general rule 

 organic diseases of the brain may be excluded if one or two days 

 pass without further development. In the horse exacerbations 



