ANIMAL MECHANISM. 67 



case from his model ; he endeavours to surpass it, and he is 

 right. To make this understood we cannot do better than 

 quote a passage in which L. Foucault compares the screw- 

 propeller of ships to the organs of swimming in fishes : 



" In our machines," said he,* " we have usually a great 

 number of parts entirely distinct one from the other, which 

 only touch each other at certain points ; in an animal, on the 

 contrary, all the parts adhere together; there is a connection 

 of tissue between any two given parts of the body. This is 

 rendered necessary by the function of nutrition which is 

 continually going on, a function to which every living being 

 is subject during the whole of its existence. We can, besides, 

 understand the absolute impossibility of obtaining a con- 

 tinued movement of rotation of one part on. another, while 

 still preserving the continuity of these two parts." 



Thus, a profound difference separates mechanisms employed 

 by nature from those invented by man ; the former are sub- 

 ject to special requirement from which the latter can be freed. 

 The muscle can only act under the condition of being attached 

 by its vessels and nerves to the rest of the organism. No 

 portion of the body, not even the bones themselves, which 

 have the least vitality, can be free from this necessity. 



One might find, in the animal organism, many other 

 mechanical appliances, the arrangement of which resembles 

 that of machines invented by man, but with differences ever 

 of the same kind as those which we have just described. 



For instance, the circulation of the blood is effected in living 

 beings by a veritable hydraulic machine, with its pump, valves, 

 and pipes. But the fundamental difference between this 

 complicated mechanism, and machines constructed by man, 

 arises from the absence of independent portions, and especially 

 of the piston. The heart is a pump without a piston, and its 

 variations of capacity are obtained by the contractility of 

 the coats of the vessels themselves. With the exception of 

 this difference, we find perfect analogies between the circula- 

 tory apparatus of animals and hydraulic motive powers. Tho 

 function of the valves is identical in both in spite of apparent 

 differences. 



* " Journal des Debats," Oct. 22, IS 45. 



