Nutritional physiology / by Percy Goldthwait Stiles.

  • Percy Goldthwait Stiles
Date:
1931
Catalogue details

Licence: In copyright

Credit: Nutritional physiology / by Percy Goldthwait Stiles. Source: Wellcome Collection.

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    ing convulsion. Clearly, then, a certain degree of central resistance is the most favorable condition for the activities of life. Any increase will tend to prevent needed adapta- tions to external changes, and any great decrease will make the reflex responses exaggerated, disorderly, and ill suited to their object. There is reason to suppose that the more frequently occurring reflexes become progressively easier to induce through a lowering of resistance in their particu- lar pathways. This brings us close to the subject of habit formation. Our emphasis has been constantly upon the advantage derived by the animal (or by man) from the possession of reflex capacities. When the environment is the accus- tomed one and the changes taking place are such as the species has often experienced, we find that almost every reflex is obviously beneficial. The reactions are such as maintain bodily equilibrium, secure nutriment, evade or defeat enemies, resist changes of temperature, all making for self-preservation. But it must be noted that an unin- telligent mechanism will act amiss in any environment which is sufficiently unlike the accustomed one. It will hardly be claimed that the reflexes exhibited by the novice on first going to sea help him in the struggle for existence. A number of reflex effects can be thought of which can scarcely be of value. Sneezing when going out into bright sunlight is one of these. Hiccups following immoderate laughter do not seem to be of any service, nor does laughter itself when induced by tickling. These instances, which on the whole have little importance, are mentioned simply to enforce the contention that the reflex mechanism, how- ever refined, is not directed in its routine performances by intelligence. Its structure determines its conduct. The finger laid upon hot iron is twitched away before the situa- tion is reasoned out, in fact, before pain is felt. Central connections exist which make the movement sure to occur, if we could rearrange those central connections we might conceive of a luckless subject who would not remove his finger from the stove, but would stand violently coughing while the injury proceeded.