Page:The American Cyclopædia (1879) Volume III.djvu/202

 196 BRAIN (DISEASES) striated bodies, teenia semicircularis, and for- nix ; the optic lobes are small, divided into two pairs, solid, and are now called the tubercula quadrigetnina ; the cerebellum is highly de- veloped, the more so as the animal approaches man, presenting the arbor vitoe in its interior ; the pons Varolii is large, and the fourth ven- tricle is completely concealed and shut in. Prof. Owen has divided the mammalia into four groups, according to the characters of the surfaces of the cerebral hemispheres ; in some the hemispheres are but feebly con- nected by the fornix and anterior commis- sure, while in the great majority the corpus callosum is added ; in the former case there is a peculiar mode of development of the young owing to the absence of the placenta. His groups are as follows : 1, tyencephala, hav- ing the hemispheres loose and disconnected, leaving exposed the olfactory ganglia, cerebel- lum, and more or less of the optic lobes, their surface smooth, or with very few anfractuosi- ties ; this includes the marsupials ; 2, lissence- phala, having a corpus eallosnm, with the cere- bellum and olfactory lobes exposed, the surface smooth, or with very few and simple convolu- tions; this includes the rodents, insectivora, cheiroptera, and edentata; 3, gyrencephala, having the cerebrum extending over more or less of the cerebellum and of the olfactory lobes, with more or less numerous convolu- tions ; this includes cetacea, pachydermata, herbivora, carnivora, and quadrumana; 4, arehencephala, embracing man only. Those wishing to pursue the study of the brain are referred to the works of Solly, Longet, Leuret, Todd and Bowman, Carpenter, Owen, Tiede- mann, Muller, and to the researches of J. Lock- hart Clarke on the "Intimate Structure of the Brain, Human and Comparative," and those of Dr. John Dean " On the Gray Substance of the Medulla Oblongata and Trapezium." BRAIN, Diseases of the. The diseases of the brain are considered as embracing, in addition to the affections seated in the cerebral sub- stance, or brain proper, those of the investing membranes or the meninges. The meningeal affections, that is, affections seated in the mem- branes, generally give rise to more or less dis- turbance of the functions of the brain, and not infrequently the disease extends from the me- ninges to the cerebral substance. So, also, affections seated primarily in the brain proper often involve secondarily the investing mem- branes. Again, there are some diseases in which the cerebral substance and the meninges are simultaneously affected. Considering the diseases of the brain in this comprehensive sense, a convenient classification of them is the following: 1, cerebral congestion; 2, cerebral anaemia; 3, cerebral haemorrhage; 4, inflam- matory affections ; 5, structural lesions ; 6, func- tional disorders. I. CEREBRAL CONGESTION. Here, as in other parts of the body, the name congestion denotes an overplus of blood (hy- persemia), which is the result, on the one hand, of an undue detention of blood, the quantity sent to the part being not necessarily greater, and perhaps even less than in health, or, on the other hand, of an undue supply of blood. An overplus of blood from detention is dis- tinguished as passive congestion, and the term active congestion denotes an undue determina- tion or supply of blood. In passive congestion the morbid accumulation is chiefly in the re- turning vessels or veins ; in active congestion, the excess of blood is in the distributing ves- sels or arteries. In either form of congestion, the vessels of both the brain substance and the meninges are abnormally filled with blood. Active congestion of the brain may be caused by undue excitation of the emotional faculties of the mind. When this is the cause, the ex- cessive functional activity of the brain attracts to the head an undue quantity of arterial blood. Another cause is the abuse of alcoholic stimu- lants. Here, too, the exciting effect of alcohol upon the brain occasions a morbid afflux to the head. An increase of the muscular walls of the left ventricle of the heart is another cause of active congestion. This is apt to be a cause when the morbid muscular growth (hypertro- phy) is not compensated for by certain valvular lesions which obviate this effect. The active congestion under these circumstances is due to the blood being sent to the head in larger quantity and with greater force than in health. Active congestion of the brain, as regards its degree, varies from an amount which consti- tutes only a slight malady to an excessive de- termination of blood leading rapidly, or even suddenly, to death. Existing in a slight or moderate degree, it gives rise to diffused pain in the head, flushing of the face, and deficient or disturbed sleep. In a more marked degree, the headache is intense and accompanied with a sense of bursting, weight, or fulness ; the sur- face of the head is hot ; the face is deeply red- dened ; the vessels of the eyes are injected ; the arteries of the temple and neck pulsate strongly, and there is inability to sleep. Ac- tive or maniacal delirium is sometimes due to active congestion. Epileptiform convulsions are also, in some cases, attributed to this con- dition. A suddenly induced active congestion is among the different conditions giving rise to an apoplectic seizure which may prove speedily fatal. Apoplexy thus induced is distinguished as congestive apoplexy. The congestion may lead gradually to loss of consciousness, or coma, which may end in death. In some of the cases of insolation, or sunstroke, the only pathologi- cal condition found after death is cerebral con- gestion. Active congestion of the brain may he diminished and often removed by appro- priate treatment. If dependent on mental ex- citement or the abuse of alcohol, the continued operation of these causes is of course, if pos- sible, to be prevented. In the rare cases of simple hypertrophy of the heart, that is, hy- pertrophy without valvular lesions, the abnor- mal power of the heart's action can be dimin-