486 Nl'MBER OF STIMULI. 



contraction = 18 to 20 impulses per second. Fig. 333, 1., represents a myogram of a 

 sustained contraction of the flexor brevis pollicis and abductor pollicis, recorded on 

 a vibrating plate. The wave-like elevations indicate the single impulses, each 

 tooth = 0*01613 second. II. is a similar curve registered by the extensor digiti tertii 

 (Landois). [Schiifer rinds that a prolonged voluntary contraction in man is an 

 incomplete tetanus produced by 8 to 13 successive nervous impulses per second. 

 About 10 per second may be taken as the average.] 



The requisite degree of shortening is obtained, by the summation of single stimuli applied to 

 the slowly contracting muscle, until the desired degree of shortening is obtained. In estimating 

 exactly the amount of movement, we generally oppose some resistance by contracting antagonistic 

 muscles, as is shown by observations on spare individuals (Briicke). 



The tetanic contractions, which occur normally in an intact body, are proved to consist of 

 a series of successive contractions, because they can give rise to secondary tetanus ( 332), which 

 may also be caused by muscles thrown into tetanus by strychnin poisoning (Lovbi). The 

 muscle-sound cannot be regarded as a proof of the oscillatory movement in tetanus, [as Helmholtz 

 has shown that this sound coincides with the resonance sound of the ear {Hering and 

 Fried rich)]. 



If a muscle be connected with a telephone, whose wires are brought into connection with two 

 needles, one placed in the tendon, and the other in the substance of the muscle, we hear a 

 sound when the muscle is thrown into tetanus, which proves that periodic vibratory processes, 

 i.e., successive contractions, occur in the muscle (Bernstein and Schonlein). The sound is most 

 distinct when the tetanising Neefs hammer of an induction machine vibrates about 50 times 

 per second ( lVcdcnski and Kronecker). 



The number of stimuli requisite to produce tetanus varies in different animals, and in 

 different muscles of the same animal. About 15 stimuli per second are required to produce 

 tetanus in the muscles of the frog (hyoglossus only 10, gastrocnemius 27); very feeble stimuli 

 (more than 20 per second) cause tetanus (Kronecker) ; the muscles of the tortoise become tetanic 

 with 2 to 3 shocks per second ; the red muscles of the rabbit by 10, the pale by over 20 

 (Kronecker and Stirling) ; muscles of birds not even with 70 (Marey) ; muscles of insects 330 

 to 340 per second (Marey). Tetanic stimulation of the muscles of the crayfish (Astacus) and 

 also in hydrophilus, may cause rhythmical contractions (Bichet), or rhythmically interrupted 

 tetanus (Schonlein). 



Curarised muscles sometimes pass into tetanus on the application of a momentary stimulus 

 (K'uhne, Hering). 



O. Soltmann found that the 2>alc muscles of new-born rabbits were rendered tetanic with 16 

 stimuli per second, so that tetanus was produced in them with the same number of shocks as in 



fatigued adult muscles. This may serve 

 partly to explain the facility with which 

 spasms occur in new-born animals. 



[The red and pale muscles of a 

 rabbit, as already shown, differ struc- 

 turally, and also in regard to their 

 blood supply (p. 458). They also differ 

 physiologically and chemically (p. 460). 

 "When both muscles are caused to con- 

 tract, by stimulating the sciatic nerve 

 Fig. 334. with a single induction shock, the 



Curves obtained from red (upper) and pale (lower) curves obtained are shown in fig. 334 ; 

 muscles of a rabbit, by stimulating the sciatic nerve the lower one from the pale, and the 

 with a single induction shock. The lowest line upper from the red muscle. The latent 

 indicates time, and is divided into T fo second period is longer, while the duration of 

 (Kronecker and Stirling). . a simple contraction of a red muscle is 



three times longer than that of a pale 

 muscle. Four stimuli per second cause an incomplete tetanus, and 10 per second a nearly com- 

 plete tetanus in the red muscles of a rabbit, while the pale muscles require 20 to 30 stimuli per 

 second to be completely tetanised. Fig. 335 shows the results produced by induction shocks 

 applied to both muscles at intervals of \ second.] 



The extent of shortening in a tetanically contracted muscle, within certain limits, is dependent 

 upon the strength of the individual stimuli but not upon their frequency. The contraction- 

 remainder after tetanus is greater the stronger the stimuli, the longer they are applied, and 

 the feebler the muscle used (Bohr). For an unweighted muscle, the height of a contraction and 

 that of tetanus are the same (v. Frcy). Only when a muscle is weighted is the height of a single 

 contraction less than by a tetanic contraction. Sometimes a stimulus applied to a muscle imme- 

 diately after tetanus produces a greater effect than it did before the tetanus (Bossbach, Bohr). 



