418 



MOTION. 



or 1 : 8 : : 120 + 122 : 1936 : = the force re- 

 sisted or employed by the glutei muscles. 



\v o :tv: : z:y, 



or 1 : 6 : : 2322 : 1936 : =:*the power exerted 

 by the quadratus femoris; 



ikd:dp::s:l* 



or 1 : 3 : : 720 : 2160. The last proportion gives 

 the force exerted by the gastrocnemius and 

 soleus muscles to sustain the weight of the man 

 together with the weight r ; now as the sum of 

 the forces exerted by the muscles /" + y + I 

 = 2 X (1936) + 2160 = 6032, and the 

 weight supported being only 120lbs., it follows 

 that the extensor muscles of the leg, to sustain 

 this weight, exert a force = 6032lbs., being 

 more than fifty times the weight. 



Force of' muscles at various stages of their 

 contraction. The variations which the force 

 of muscles undergoes in different states of their 

 contraction have not yet been thoroughly in- 

 vestigated ; though it is a subject not only 

 susceptible of being pretty accurately deter- 

 mined, but also leads us to form a more cor- 

 rect hypothesis of the laws which regulate the 

 contraction of the muscular fibres, and of the 

 physical operation of the vital agents which 

 are the immediate causes of the contraction. 



The force of muscles, according to the ex- 

 periments of Schwann, increases with their 

 length, and vice versa. His experiments were 

 made on the gastrocnemius muscle of a frog. 

 The apparatus which he employed consisted 

 of a board, to which the frog was fixed, 

 with the thigh in the horizontal position, the 

 leg being raised so as to be perpendicular to 

 the board, and the foot again flexed to the 

 horizontal position, in which posture the limb 

 was firmly fixed; a rod or beam was suspended 

 over the board and made capable of turning 

 upon it as its axis of oscillation. This balance 

 beam was unequally divided with respect to its 

 axis of motion, one arm being to the other as 

 1 to 6. To the longest arm of the beam a 

 scale was separated; to the other arm the tendo 

 Achillis (which had been carefully exposed 

 and detached from the heel) was attached by 

 means of a thread; by this method a very 

 small contraction of the muscle caused the 

 other end of the beam to revolve through a 

 much greater space, so that the slightest con- 

 traction of the muscle became very apparent. 

 The ischiatic nerve was then laid bare, cut 

 through high up in the thigh, and drawn out, 

 great care being taken not to injure the sur- 

 rounding vessels. The nerve was then laid 

 upon two wires, connected with a galvanic 

 battery, consisting of a single pair of plates, 

 one of the wires being connected with one pole 

 of the battery, and the other made to commu- 

 nicate with the opposite pole by using a slight 

 pressure upon it. The skin was left entire, 

 except where the tendon and nerve were ex- 

 posed. By this simple apparatus, Schwann 

 observed that the force of the muscle was at a 

 maximum when at its greatest elongation, and 



* This computation differs from that in the 53d 

 prop, of Borelli; where he has substituted new 

 and arbitrary values for s and z in the two last pro- 

 portions, which diminish the values of y and /. 



at a minimum at its greatest contraction. In 

 a series of five experiments, which were repeated 

 at equal intervals, the forces of the muscles at 

 different lengths were in the following propor- 

 tions : 



J_ end of experiment. 



f 13.5 



) 100 18.8... 



\ 200 23.4... 



v. end of exp. 14.4 



f 13.7 



50 18.7.. . 



{ 100 20.3... 



I 50 17.7 



[_ end of exp. 14.1 



f U * * 1 u>O 



2 100 19.1. 



C200 23.2 



.4.3 

 .4.6 



.4.3 

 .2.1 



.5.6 

 .4.1 



4. 



5. 



This table shows that twice the comparative 

 length coincides with twice the force of the 

 muscle, and that at its greatest contraction the 

 force = 0. In the first two experiments the 

 increase of force and length of muscle were 

 uniform ; but in the last three the ratios of the 

 force and the length varied; the earliest ex- 

 periment, however, was performed when the 

 animal might be supposed to be nearest to 

 its normal condition, and therefore when the re- 

 sult approximated most nearly to the healthy 

 play of the muscle. 



These experiments of Schwann are opposed 

 to the hypotheses of Prevostand Dumas, as well 

 as to those of Meissner, who regard the pheno- 

 mena of muscular contraction to be due to the 

 force of electric attraction, but as the latter in- 

 creases in force the more nearly the attracted bo- 

 dies approach each other, and decreases as they 

 recede in the inverse ratio of the square of the 

 distance, and as the force of elastic bodies 

 varies in a ratio differing from that of muscles, 

 when their length and force affecting them 

 vary, we conclude that the contraction of 

 muscles does not depend upon any of the 

 known laws connected either with electro- 

 dynamics or the forces regulating the molecules 

 of elastic matter. 



If we conclude from the experiments of 

 Bergolotti, Mayo, and Prevost and Dumas, 

 that the contraction of muscles is unaccom- 

 panied by a diminution of bulk, and that the 

 aggregate molecules present equal volumes and 

 are at equal distances fiom each other, whe- 

 ther contracted or not, the electric force would 

 remain constant, whilst the muscular force 

 varied; or if with Professors Gruithuisen and 



