328 OP THE PRIMARY TISSUES OF THE HUMAN BODY. 



rigidity had supervened. Many circumstances indicate that these movements 

 were due to the inherent contractility of the muscles, and were not in any de- 

 gree dependent upon the operation of the nervous system; and Dr. Dowler 

 proved experimentally, by completely separating limbs which exhibited these 

 movements, from the trunk of the body, that the influence of the nervous cen- 

 tres was not in any degree essential to their production. 1 A phenomenon of a 

 similar order has been observed by Dr. Stokes, 3 even during the life of the sub- 

 ject. In various cases of phthisis and of other exhausting diseases, a sharp tap 

 with the fingers on any muscular part is instantly followed by a contraction of 

 the part which receives the irritation, evidenced by the rise of a defined firm 

 swelling, which is often so prominent as to throw a shadow along the skin, and 

 which endures for several seconds before it gradually subsides. The complete 

 limitation of this contraction to the part struck, is sufficient evidence that it 

 must be attributed to direct stimulation of the muscle itself, and not to a 

 " reflex" action of the nervous system. 



329. A curious question has been lately raised, the decision on which is of 

 some importance in our determination of the nature of the force, by which the 

 contraction of muscles is occasioned. This is whether the power of a muscle 

 is greater or less at different degrees of contraction, the same stimulus being 

 applied. This seems to have been determined by the ingeniously-devised experi- 

 ments of Schwann. 3 He contrived an apparatus, which should accurately 

 measure the length of the muscle, and, at the same time, the weight which it 

 would balance by its contraction. Having caused the muscle of a Frog to 

 shorten to its extreme point, by the stimulus of galvanism applied to the nerve, 

 so that no further stimulation could lift a weight placed in the opposite scale, 

 he allowed the muscle to relax until it was extended to a certain point, and then 

 ascertained the weight which would balance its power. The same was several 

 times repeated, as in the following manner : The length of the muscle in its 

 extreme state of contraction, at which no additional force could be exerted by 

 it, being represented by 14, it was found that, when it had been extended to 17, 

 it would balance a weight of 60; when its length increased to 19.6, it would 

 balance a weight of 120; and at 22.5, it would balance 180. In another ex- 

 periment, the muscle at 13.5, balanced 0; at 18.8, it balanced 100; and at 

 23.4, it balanced 200. Hence it appears that a uniform increase of force corre- 

 sponds with a nearly uniform increase in the length of the muscle ; or in other 

 words, that when the muscle is nearly at its full length, its contractile power is 

 the greatest. In later experiments upon the same muscle, this uniform ratio 

 seemed to be departed from ; but, by comparing the results in a considerable 

 number of instances, it was constantly found that, in those experiments which 

 were performed the soonest after the preparation of the frog, and in which, 

 therefore, the normal conditions of the system were the least disturbed, the 

 ratio was very closely maintained. It has been ascertained by Valentin, on 

 repeating these experiments, that, by repeated equal irritations, the strength of 

 the muscles in decapitated frogs decreases in a regular and corresponding ratio; 

 losing the same amount in each successive period of time. He also found that, 



1 It is remarkable that, in the case of both these diseases, the temperature of the corpse 

 usually rises considerably after death, so as to approach its usual standard when the body 

 has been previously cooled down much below it, and to rise considerably higher when 

 there has been no previous depression (CHAP. xin.). Moreover, the cadaveric rigidity is 

 usually long in coming on ; being sometimes postponed for many days after death from 

 Cholera. 



2 "On Diseases of the Chest," p. 397. 



3 Muller's "Elements of Physiology," translated by Baly, p. 903. 



