250 PHENOMENA OF FLIGHT IN THE ANIMAL KINGDOM. 



pectoral muscle extends about 3 centimeters in its longest direction. If 

 we supposed tlie muscular force applied to the middle of this line of 

 attachment, the leverage of the power would he about 17 millimeters. 

 The weight lifted and the muscular exertion, both multiplied l)y their 

 respective leverage, are equivalent to each other. It follows that the 

 real value of the power of the bird is ~^^^ ; which gives 12^^.000 for 

 the entire force of the great pectoral muscle. Dividing this number by 

 9 '^ 1, 7, Avhich represents the surface of the section of the muscle, Ave 

 obtain for each bundle of muscle of the bird, having one square centi- 

 meter of sectional surface, a power of 1,298 grams. 



The snuill result which I have obtained may be affected with certain 

 causes of error. In the first place, I had not cut the tendon of the 

 middle pectoral muscle which elevates the wing. It may therefore be 

 objected that, as the electric currents have radiated throughout tlie 

 deeper regions of the thoracic nuiscles, and have excited the elevator 

 muscle of the wing of which the action is antagonistic to that of the 

 great pectoral, that is to say, acting in the same direction as the weight, 

 has sensibly diminished the force necessary to neutralize the power of 

 the former muscle. It may also be said that the electric agent cannot 

 produce as powerful an effort in the muscle as that evoked by the will. 

 Admitting that these objections are all well founded, let us double, or 

 even quadruple the force which I have assigned to the muscle, and still 

 we shall not equal the result that Koster attributes to the specific force 

 of the muscle of man. Thus, in spite of the want of precision in the 

 experiments which I have made, I believe the proofs can be found in 

 them that there does not exist in the muscles of birds a notably greater 

 power than that found in those of other animals. 



One of the most striking peculiarities of the action of the muscles of 

 birds is the extreme rapidity with which in them is evolved force. Of the 

 different kinds of animals of which I have determined the character of 

 their muscular action, the birds have exhibited the most rapid move- 

 ments. The curve of motion which a muscle produces can be registered 

 by myography, and thus the duration of its contraction and relaxation 

 can be estimated. If we make use of electricity or any instantaneous 

 motor, on the nerve of a muscle, or on the muscle itself, a motion is 

 evoked of which the duration varies according to the species of animal 

 experimented upon. This motion, which I have called the mnscuJar 

 shoeJc, to distinguish it from the prolonged contraction which takes place 

 under other circumstances, lasts in the muscles of the tortoise a second 

 or more ; in man it lasts at least six or eight hundredths of a second, 

 and in birds it endures about four-hundredths of a second. This rapidity 

 is an indispensable condition of flight. In fact, the descending wing 

 can only olDtain sufficient hold on the air by moving with great speed. 

 The resistance of the air to a plane surface pressing upon it sensibly 

 increases as the square of the velocity with which the plane descends. 

 To have powerful muscles would be of no use to the bird if they acted 

 slowly ; their force would be wasted for want of resistance, and no 

 results would be produced. It is otherwise with terrestrial animals 

 which run or gallop over the ground; they definitely utilize their mus- 

 cular force in work by reason of the great resistance which they en- 

 counter. Eapid motion is necessary even to fishes ; the water in which 

 they exist resists in proportion to the rapidity with which it is struck by 

 the tail and fins. If the muscular action is quick in the case of fishes, 

 it must be much quicker in that of birds, which move in a much more 

 rarefied medium. To explain the i)roduction of such rapid motion as 



