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AN AMERICAN TEXT-BOOK OE PHYSIOLOGY 



The fact that the second contraction is higher if it starts during the ascent 

 of the first, may be explained as due to a summation of the condition of ex- 



Fk;. 55.— Effect of support on height of contractions (after Von Frey) : a, gastrocnemius muscle of a 

 frog, separate contractions, tetanus, separate contractions, and group of supported contractions ; weight 

 10.5 grams ; 6, the same, by weight of 0.5 grams. 



citation awakened by the two irritants, and hence the liberation of a greater 

 amount of energy. Nevertheless, the increased irritability, indicated by stair- 

 case contractions, and the summation of excitation effects which occur by rapidly 

 repeated excitations, shown by the above experiment, do not suffice to wholly 

 explain the great shortening of the muscle seen in tetanus. Helmholtz' idea, 

 that there is a support afforded by the first contraction to the second, must 

 also play an important part, and we must turn to this for the completion of the 

 explanation of the great height acquired by the tetanus curve. 



Effect of Support on the Height of Contractions. — Von Kries 1 and Von 

 Frey 2 found that, in general, the shorter the distance the muscle has. to raise 

 a weight, the higher it can contract, and that if a muscle be excited at a regu- 

 lar rate, and the support for the weight be raised between each of the succeed- 

 ing contractions, at a certain height of the support the contractions may be 

 as high as during tetanus (see Fig. 55) This effect can be got with a fresh 

 muscle when the interval between the excitations is such that there can be no 

 summation in Helmholtz' sense. 



The importance of this discovery to our understanding of tetanus is very 

 great, for it has been found that if an unsupported muscle be rapidly excited, 

 effects are observed which closely resemble those obtained by the aid of a sup- 

 port; this we have seen in the experiments recorded in Figures 50, 51, p. 115*. 

 After a certain amount of excitation, a change occurs in the condition of a 

 muscle, owing to which it acts as if it had received an upward push, and as 

 if a new force had been developed within it, which aids the ordinary con- 

 traction process in raising the weight. The new aid to high contraction is 

 the support afforded by the developing condition of contracture. That con- 



1 Archir Jar Analmnie. und 1'hy.vnlor/ie, 188(5. - Ibid., 1887. 



