EFFECTS "OF PRESSURE ON THE BRAIN. 



729 



in parts where ascending veins convey blood from descending arteries, whereby the hydrostatic 

 pressure and gravity aid the circulation, but here gravitation is opposed to the flow of blood in the 

 cerebral veins. This will help to explain the occurrence of thrombosis in these vessels. Some 

 of the veins on the surface communicate with intracranial veins, e.g., those of the nose, the 

 facial through the ophthalmic, mastoid veins, and veins of the diploce. Hence, morbid processes 

 affecting the scalp (erysipelas), ear (caries), or face (carbuncle) may readily affect intracranial 

 structures (Goivers).] 



If a person who has been in bed for a long time, and whose blood is small in amount, be 

 suddenly raised into the erect position, cerebral anaemia is not unfrequently produced, owing to 

 hydrostatic causes. At the same time, there may be loss of consciousness and impairment of 

 the senses. Liebermeister regards the thyroid gland as a collateral blood-reservoir which 

 empties its blood towards the head during such changes of the position of the body. Perhaps 

 this may explain the swelling of the thyroid as a compensatory act, when the heart beats 

 violently, and the brain is surcharged with blood ( 103, III., and 371). Very violent 

 muscular exertion, as well as marked activity of other organs, causes a very considerable fall of 

 the blood-pressure in the carotid. 



Pressure on the Brain. The brain and the fluid surrounding it are constantly subjected to 

 a certain mean pressure, which must ultimately depend upon the blood-pressure within the 

 vascular system, The investigations of Naunyn and Schreiber on the cerebral pressure (or 

 cerebro -spinal pressure) showed that the pressure must be slightly less than the pressure 

 within the carotid, before the symptoms proper to pressure on the brain occur. These are, 

 sudden attacks of headache, with vertigo, or it may be loss of consciousness, vomiting, slowing 

 of the pulse, slow and shallow respiration, convulsions while the pressure of the cerebro 



Fig. 511. 

 Transverse section of the cerebrum behind the optic chiasma. Arteries of the corpus striatum. 

 C h, optic chiasma ; B, section of optic tract ; L, lenticular nucleus ; I, internal capsule ; 

 C, caudate nucleus ; E, external capsule ; T, claustrum ; R, convolutions of the island of 

 Reil ; V, V, section of the lateral ventricles ; P, P, pillars of the fornix ; 0, grey substance 

 of the third ventricle. Vascular areas I, anterior cerebral artery ; II, Sylvian artery ; 

 III, posterior cerebral artery ; 1, internal carotid ; 2, Sylvian, 3, anterior cerebral artery ; 

 4, 4, lenticulo-striate arteries ; 5, 5, lenticular arteries. 



spinal fluid is increased. The cause of these phenomena lies in the anaemia of the brain. If 

 the pressure is moderate, the above-named symptoms may remain latent ; nevertheless, 

 disturbances of the nutrition of the brain occur, with consecutive phenomena, such as 

 persistent slight headache, feeling of vertigo, muscular weakness, and disturbances of vision 

 (owing to neuro-retinitis with choked disc). Increase of the blood-pressure diminishes the 

 symptoms, while diminution of the blood-pressure causes more pronounced phenomena of 

 cerebro-spinal pressure. In the dog, pain begins with a pressure of 70 to 80 mm. Hg. 

 Consciousness is abolisJied when the pressure is higher, and at 80 to 100 mm. spasms take place. 

 A pressure of 100 to 120 mm. causes sloiving of the pulse, owing to stimulation of the vagus at 

 its origin ; the respirations are temporarily accelerated and then diminish. Long-continued 

 severe compression always, sooner or later, ends fatally. The blood-pressure at first is increased, 

 owing to reflex stimulation of the vaso-motor centre from the pressure stimulating the sensory 

 nerves ; ultimately, the blood-pressure falls, and the pulse becomes very slow. Irregular 

 variations in the blood -pressure point to a direct central stimulation of the vaso-motor centre 



