Diseases of the nervous system : a text-book of neurology and psychiatry / by Smith Ely Jelliffe and William A. White.

  • Jelliffe, Smith Ely, 1866-1945.
Date:
[1919], ©1919
Catalogue details

Licence: Public Domain Mark

Credit: Diseases of the nervous system : a text-book of neurology and psychiatry / by Smith Ely Jelliffe and William A. White. Source: Wellcome Collection.

    24/1050 (page 18)
    Right here, in the term “phylogenetically older,” is the key to the principle of classification—a principle that has long governed in the bio¬ logical sciences, the simpler and older merging by insensible gradations into the more complex and more recent. It has taken long periods of time and the accumulation of great masses of detailed observations before those facts of wider bearing have emerged that have served to bring all this material together under wider generalizations. The older hypotheses have become more and more inadequate; in their prime they were useful, but as with all hypotheses, which are solely functions of thinking, their present aspect of staleness is a sign of possible progress. For a long time it has been asserted that the nervous sytem is the means by which all of the several parts of the human unit are integrated by a species of complicated adjustments to given ends. It can be perceived how this integration is actually brought to pass by means of the vegetative nervous system and the chemical regulators of metabolism, at a physicochemical level, and how by the successive compounding of reflexes at the sensorimotor level, the human unit is further integrated, so that it can as a whole work more consistently toward broadly defined goals, the integration manifesting itself at suc¬ cessively higher and higher levels in the history of the individual and of the species. Viewed in this way the individual is seen struggling along the path of evolution in constant conflict with an inherent inertia that would keep it at a given level, but gradually advancing by a series of give-and-take compromises that finally bring it to better adjustment with its environment at ever higher levels of integration. Sherrington has beautifully illustrated this integrative action of the nervous system in the simple reflex with its innervation of agonists on the one hand and antagonists on the other, and the channelling of final common pathways for nervous discharge. This law of conflicting tendencies, pathways of opposites—ambivalence—where the final issue for higher integrations is made possible at the sensorimotor level by the tension of reciprocal innervations, is found also to be the rule in the vegetative nervous system, with its double set of pharmaco- dvnamically demonstrated balancing elements, mediated, at least in part, by equally opposed, stimulogenic chemical substances secreted by the endocrinous glands, the hormones. Finally an analogous ambivalent mechanism is seen working at the highest, the most complex level, the psychic, which determines conduct vith the assistance of the phenomenon called consciousness, in which a ps\ chological symbolism is found replacing sensory and motor neurons, and exciting and inhibiting hormones. ^or practical purposes, then, the nervous system may be divided into these three levels of activity, the vegetative, the sensorimotor and the psychic. 1 lib threefold division of the reactions of the nervous system is the fundamental basis on which a classification may be founded. The