DISEASES OF THE BRAIX. 



symptom is very generally regarded as a sign of " increased pressure 

 of blood to the head," although it really indicates that the flow of blood 

 into the skull is obstructed ; we may at any moment induce the same 

 phenomenon in the artery of the finger by tying a string tightly 

 around the end of the finger. All diseases of the brain and its mem- 

 branes affecting the space in the skull enough to obstruct the afflux 

 of blood from the afferent vessels, hence not only large effusions of 

 blood, but also abundant exudations and transudations, large tumors, 

 etc., are accompanied by increased pulsation of the carotids. If we 

 find this symptom, when there is no hypertrophy of the left ventricle, 

 nor corresponding pulsation in other arteries, it will, in doubtful 

 cases, be a great aid to the diagnosis of some brain-disease encroach- 

 ing on the cranial cavity. In my clinic my pupils have frequently had 

 an opportunity of satisfying themselves of the correctness of the indi- 

 cation and of the great diagnostic value of this symptom. If we re- 

 gard the physical conditions, we see that anaemia, at all events arte- 

 rial anaemia', of the brain can never result from rupture of the capil- 

 laries ; for the escape of blood from the ruptured capillaries can only 

 last till the tension of the contents of the skull equals that of the 

 blood in the capillaries. In accordance with this we see that the apo- 

 plectic fit does not occur in capillary haemorrhage. If, on the other 

 hand, an artery be ruptured, and the bleeding does not soon cease 

 from some other cause, the tension in the surrounding parts finally 

 becomes as great as it is in the artery ; and, as it is greater there than 

 in the capillaries, the latter must be compressed and become impassa- 

 ble for the arterial blood. In accordance with this, apoplectic fits al- 

 most always accompany arterial haemorrhages of any extent. If we 

 analyze the above symptoms of the apoplectic fit, we find that, while 

 it lasts, the functions of both sides of the cerebrum are lost. The pa- 

 tients have no feeling, even on the strongest peripheral irritation; 

 they cannot make the slightest motion, and consciousness is entirely 

 lost. On the other hand, those portions of the brain through which 

 acts indispensable to life, especially respiration, are performed, retain 

 their functional power. This is, apparently, because the falx protects 

 the opposite hemisphere less, from the compression of the capillaries 

 by the extravasation, than the tentorium does the medulla oblongata. 

 Effusions of blood below the tentorium, even when slight, are very 

 dangerous, because in them the medulla oblongata is not thus pro- 

 tected, and its functions are readily disturbed by compression of its 

 capillaries. I shall not attempt to decide whether or not the slowness 

 of the pulse, the diminished frequency of respiration, and the contrac- 

 tion of the pupil, observed during apoplectic fits from effusions above 

 the tentorium, are due to increased excitement of the vagus and oculo- 



