A text-book of human physiology (1906) (14747424006)

Identifier: textbookofhumanp00tige (find matches)

Title: A text-book of human physiology

Year: 1906 (1900s)

Authors: Tigerstedt, Robert, 1853-1923 Murlin, John R. (John Raymond), b. 1874, tr

Subjects: Physiology

Publisher: New York and London, D. Appleton and Co.

Contributing Library: Columbia University Libraries

Digitizing Sponsor: Open Knowledge Commons

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ation,although, so far as nuisele alone is concerned, the excitation of large massesappears to depend upon sudden changes at the place of direct stimulation.Moreover, the law must take into account the nature of the irritable tissue:2G 422 THE FUNCTIONS OF CROSS-STRIATED MUSCLES the more irritable it is, the more do the visihle phenomena of continuousexcitation remain in the background, whereas the effects of variation in thecurrent become the more apparent (Biedermann). For all irritable tissues there is a minimum duration of the electric cur-rent necessary to give a stimulus. Other things being equal, the more thistime is shortened, the less becomes the stimulating effect until finally it failsaltogether. The length of time necessary to produce the maximal effect de-pends primarily on the strength of the current. The greater the strengththe shorter the time may be. A constant current of medium strength re-quires 0.016 second to produce its maximal effect on motor nerves (J, Konig) ;

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Fig. 160.—A convenient arrangement of the apparatus for sending induction shocks througha muscle is shown in this Figure. BC, the battery cell; K, key for closing and opening theprimary current. When the wires are connected with binding posts 1 and 2 of the inductioncoil, single make and break shocks are obtained from the secondary coil and are conveyedby the wires connected therewith to the muscle. When the wires are connected with bindingposts 1 and 3 of the induction coil the automatic interrupter is brought into play and a seriesof rapidly repeated (tetanic) shocks is obtained. By means of hand electrodes connected withthe secondary end of the induction coil, stimuli may be applied in various other ways. no contractions are obtained if the time be reduced below 0.002 second. In-duction shocks are still shorter than this; nevertheless, because of their hightension they are the most effective stimuli for the nerves. So far we have considered only the effects of currents suddenly t

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1906

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