PHENOMENA OF FLIGHT IN THE ANIMAL KINGDOM. 249 



exerted by birds during flight, it would be necessary in the first place 

 to demand from physiological experimentation all the facts of the prob- 

 lem. The estimate in question presupposes an acquaintance with the 

 motions of the wings, with their form, their extent, and their rapidity 

 at each instant ; it also supposes a knowledge of the extent of the 

 surface of the wings, their curve, and the angle at which they strike 

 the air. This problem, then, will iierhaps be the last which we can 

 hope to solve; but we can study at present, from other points of view, 

 the strength of the muscles of the bird, and estimate some of the char- 

 acteristics with which it is manifested. 



A measure of the maximum effort which the muscles of birds can de- 

 velop can already be obtained experimentally. This measure may indeed 

 fail to correspond with the efforts developed in flight, but it may prevent 

 us from falling into the exaggeration which would attribute to the mus- 

 cles of the bird a force superior to the maximum effort o£ which they 

 are capable. 



Of the static force of the mnscles of birds. — In physiology the static force 

 developed by a muscle is measiired by seeking the maximum weight 

 which this muscle can raise. This determination has been made bj- 

 Weber,* on the muscles of the frog; by Henke and Kuortz,t and since 

 by Koster,! on the muscles of man. The maximum weight in these ex- 

 periments was about one kilogram i^er square centimeter of muscular 

 section, according to "Weber; of five to Henke and Kuortz; of seven, ac- 

 cording to Koster. If the estimates of Borelli, and even those of Xavier, 

 were correct, we ought to find in the muscles of birds a much more 

 considerable static force. On the contrary, it does not appear to me 

 that this force surpnsses that of the muscles of the mammalia. I have 

 already shown that the weight of one kilogram, placed on the wing of 

 a pigeon at the articulation of the arm with the fore-arm, cannot be 

 raised by the voluntary efforts of the animal ; also, in certain experi- 

 ments in which we hold a bird immovable, an excellent means of testing 

 the weight consists in putting the bird on its back, the wings extended, 

 and attaching to each wing a bag containing a kilogram of shot. 



I wished, however, to have a more precise measure of the strength of 

 the p«?ctoral muscles. For this purpose a hoodwinked harrier was 

 placed on its back in the position just described. The application of the 

 hood plunges these animals into a sort of trance, during which all sorts 

 of operations can be performed on them without their betraying anj^ 

 unpleasant sensation, except by reflex movements. I denuded the great 

 pectoral and the humeral region, tied the artery, and disarticulated the 

 first joint, removing the remainder of the wing. I then fixed a cord tc 

 the extremity of the humerus, and at the end of this cord the basin of 

 a balance, into which shot was poured. The body of the bird being 

 perfectly motionless I excited the muscle by inducing interrupted cur- 

 rents of electricity, and while artificial tetanus was produced, an assist- 

 ant added more shot, until the force of contraction of the muscle was sur- 

 mounted. At this moment the weight supported was 2 kilograms, 380 

 grams. Now, the arm of the lever at the end of which this weight had 

 been placed was of the same length as the humerus, that is, about 9 cen- 

 timeters, the measurement being the length between the attachment of 

 the cord and the center of motion of the liumeral articulation. The arm 

 to which the power is applied is evidently much shorter, and is more 

 difii(!ult to measure. In the first place, the attachment of the great 



* Wagner's Handworterbucli der Pliysiologie. 



t Die grosse der absoluteu rausskelkraft in Heule and Pfcufer, t. xxiv. 



t Aichives netiiLandaises, 1866, ]). 11. 



