HYPEILEMIA OF THE BRAIN AND ITS MEMBRANES. 181 



grouped as whitish, opaque excrescences of the arachnoid, coming par- 

 ticularly along the sides of the longitudinal sinus. The pressure that 

 they exercise on the dura mater separates its filaments, so that they 

 perforate it ; by further pressure they also cause atrophy of the bone, 

 and they are then found embedded in little fossse in the skull. Micro- 

 scopically, they consist of connective tissue ; occasionally they contain 

 fat and chalky salts. 



SYMPTOMS AND COURSE. Before taking up the symptomatology 

 of hyperaemia of the brain, I shall warn against the wide-spread error, 

 so injurious to the patient, of considering all cases of disturbance of 

 function of the brain, where severe structural changes can be excluded, 

 as due to hyperaemia (or anaemia). 



Thus, the disturbance of the cerebral functions in fever is not due 

 to increased afflux of blood to the brain from excited action of the 

 heart ; but, as we have repeatedly pointed out, it depends partly on 

 the high temperature of the blood in the cerebral vessels, partly on its 

 abnormal quality, the " feverish state," a necessary result of the in- 

 creased transformation of tissue during the fever. Delirium and other 

 severe cerebral troubles are most common in the so-called asthenic 

 fevers, just where the increase of bodily temperature and the produc- 

 tion of warmth attain the highest grade, while the heart's action is 

 hastened, but weakened, and there is no fluxion to the brain. 



According to the observations made during the last war, as well 

 as from the valuable investigations and experiments of Obernier, the 

 symptoms of sun-stroke, or insolatio, do not, as was formerly sup- 

 posed, depend on hyperaemia of the brain, induced by the action of 

 the sun's rays on the head. The symptoms of this disease consist in 

 a paralysis of all the functions of the brain, occurring either suddenly 

 or gradually. In the latter case the paralysis is preceded by excite- 

 ment, delirium, and other symptoms of cerebral irritation. It has been 

 determined that, in our zone at least, the action of the sun's hot rays 

 is not alone sufficient to induce these severe attacks, but that they 

 only occur when individuals are subjected to great fatigue, on a very 

 hot day, particularly if, at the same time, they sweat very little, be- 

 cause they do not drink enough. We may assume that, under such 

 circumstances, while the radiation of heat is limited on account of the 

 high temperature of the surrounding atmosphere, while the production 

 of heat is increased by the active muscular exercise, and the coolness 

 induced by free perspiration is limited, there is an overheating of the 

 body, an increase of the bodily temperature to a height incompatible 

 with life. "We have already sufficiently explained the significance of 

 the fulness of the veins of the meninges, which is found on autopsy ic 

 cases of sun-stroke. 



