214 ANIMAL MECHANISM. 



movement, the weight supported was 2 kilogrammes 380 

 grammes (about 6 '3 8 Ibs. troy). 



If we take into account the unequal length of the arms of 

 the lever, on the side of the power and that of the resistance, 

 we find that the pectoral muscle had been able to produce a 

 total effort of 12 kilogrammes 600 grammes (about 33'78 Ibs. 

 troy), which would correspond with a traction of 1298 

 grammes (3 - C6 Ibs. troy) for each square centimetre of the 

 transverse section of the muscle. 



A pigeon placed under the same conditions has given, as its 

 entire effort, a weight of 4860 grammes, which, according to 

 the transverse section of its muscle, raised to 1400 grammes 

 the effort which each muscular bundle could develop for every 

 square centimetre of section. 



If we admit that the electrical action employed in these 

 experiments to make the muscles contract, develops an effort 

 less than that which is caused by the will, it is not less true 

 that these estimates, which are less than those which we 

 generally obtain in the muscles of mammals under the same 

 conditions, do not authorize us in recognizing in the bird any 

 special muscular power. 



Lastly, if we were to take into account in this estimate 

 the laws of thermo -dynamics, we might affirm that the bird 

 would not develop in flight a very especial amount of work. 



All work, in fact, can only be performed with a certain 

 waste of substance, and if the act of flying involved a great 

 expenditure of work, we ought to find a notable diminution 

 of weight in a bird when it returns from a long flight. Nothing 

 of this kind is observed. Persons who train carrier pigeons 

 have given us information on this point, from which we gather 

 that a bird which has traversed in a single flight a distance ot 

 fifty leagues (which it seems to do without taking any food), 

 weighs only a few grammes less than at its departure. It 

 would be interesting to make these experiments again with 

 giviter exactitude. 



Of the rnjiiility of the muscular actions of birds. One of the 

 most striking peculiarities in the action of a bird's muscles 

 is the extreme rapidity with which force is engendered in 

 them. Among the different ^ cies ut animals \\ hose muscular 



