62 



purpose of depositing its spawn, often encoun- 

 ters cataracts of great height, and which 

 would seem to render farther progress impos- 

 sible. By means, however, of a powerfully 

 muscular tail and elastic spine it is enabled to 

 surmount those obstacles ; resting one side 

 upon a solid fulcrum, it seizes its tail between 

 its teeth, and thus draws itself into an arch of 

 amazing tension ; then suddenly letting go its 

 hold, and thus freeing the elastic spring which 

 its body represented, it is thrown into the air, 

 often, as Twiss has seen in Ballyshannon in 

 Ireland, to a height of twelve or fifteen feet, 

 and falls beyond the obstacle which had op- 

 posed it. 



5. Elasticity becomes occasionally in the 

 animal machine a means of dividing muscular 

 force, and thus transferring it from one portion 

 of an apparatus to another. The muscles of 

 inspiration are, if we may use the word, too 

 strong for their opponents, and hence it be- 

 comes necessary to transfer a portion of their 

 superfluous strength to the weaker set. This 

 is effected by means of the elastic cartilages 

 which connect the ribs and sternum. The m- 

 spiratory muscles in enlarging the thorax act 

 with such a force that they not only elevate the 

 ribs, but even stretch and twist the cartilages, 

 and hence no sooner is inspiration completed 

 than elasticity comes into play, tendingto depress 

 the ribs and thus to assist the weaker muscles. 

 But we must not fall into the error of suppo- 

 sing that elastii ity is in this case a substitute 

 for muscularity, and much less that it is in 

 itself a source of power. The only power 

 exercised by it is that which it has just bor- 

 rowed from the inspiratory muscles : had not 

 the elasticity of the cartilages been set in action 

 by this external agency, it would, like the elas- 

 ticity of the watch-spring under the same cir- 

 cumstances, have remained for ever dormant. 

 In those interesting discussions which have 

 arisen of late years relative to what is termed 

 the suction power of the heart, we apprehend 

 that much error has arisen from overlooking 

 tliis simple law of elasticity. That doctine 

 will of course be fully stated and examined 

 in its proper place ; at present we shall merely 

 observe that it was first regularly put forward 

 in the admirable work of Dr. Wilson Philip, 

 that it was followed up and explained by Dr. 

 Carson, and that these views were regarded by 

 Laennec with such respect that he pronounces 

 their discovery the most important step made 

 in this department of physiology since the 

 time of Harvey. The heart, it is said, is not 

 merely a forcing pump which by the contrac- 

 tion of its ventricle propels the blood through- 

 out the arteries ; it is likewise a suction pump, 

 for by the expansion of the auricles it draws in 

 trie blood from the veins. Now this expansive 

 force, if indeed it exist at all, is, we are quite 

 satisfied, merely the effect of the heart's elas- 

 ticity; for the reasonings of those who attempt 

 to prove it of a specific nature are evidently 

 insufficient. In this point of view the heart's 

 expansion cannot be regarded as a new and 

 independent power; if that organ be really 



REGION OF THE ELBOW. 



elastic, then the muscular force of its systole 

 must be greater than it would otherwise have 

 been, for it has not only to propel the blood 

 through the arterial system, but likewise to 

 overcome the resisting elasticity of its own 

 structure: this suction power of the heart is 

 then merely the recoil of the surplus force; 

 what is gained upon the one hand is lost upon 

 the other; and hence elasticity in this instance 

 cannot be regarded as an independent prin- 

 ciple contributing to the blood's motion, but 

 merely as a means of dividing muscular power 

 and transferring a portion of it from the begin- 

 ning of the arterial to the end of the venous 

 system. 



6. An interesting application of elasticity in 

 the animal machine is to convert an occasional 

 or intermitting force into a continued one. As 

 human ingenuity has long since discovered the 

 application of this principle, we may see it 

 employed in many mechanical contrivances. 

 In the common fire-engine, for instance, we 

 observe that though it is worked by interrupted 

 jerks, yet the water issues from its pipe, not 

 per saltum as we should have expected, but in 

 one uniform and continued stream. This is 

 effected by causing the fluid to pass, in the first 

 instance, into a hermetically sealed vessel con- 

 taining a portion of atmospheric air : the accu- 

 mulation of the water presses the air into a 

 smaller space, but in doing so it is reacted 

 upon by the elasticity of that gas, which may 

 thus be considered as a powerfully elastic 

 spring exerting upon the surface of the water 

 an uniform and continual pressure. The very 

 same principle is employed in the mechanism 

 of the arterial system. Upon opening one of 

 the small arteries we perceive that the blood 

 does not flow per saltum as in those which are 

 nearer to the heart, but issues in an uniform 

 and uninterrupted stream. The intermitting 

 action of the heart has in fact been converted 

 into a continued one by means of the elasticity 

 of the arterial tissue. We might indeed say 

 with truth that the blood in these small arteries 

 is not directly propelled by the heart at all; 

 the force of that organ is expended in distend- 

 ing the larger elastic arteries, as the force in the 

 fire-engine is expended in compressing the air. 

 The immediate cause of motion is in the one 

 case the reaction of the elastic air, and in the 

 other the reaction of the elactic artery. 



For the BIBLIOGRAPHY of this article, see that 

 of FIBROUS TISSUE and MUSCLE. 



(John E. Brenan.) 



ELBOW, REGION OF THE ; fold or 

 bend of the arm. (Fr. pit du bras; coutle.) The 

 region of the elbow is situated at the angular 

 union of the arm with the fore-arm, and con- 

 tains the luunero-cubital articulation and the 

 various organs which surround it : the extent 

 of this region may be determined, superiorly 

 by a circular line at a finger's breadth above 

 the internal condyle, and inferiorly by a similar 

 line at two fingers' breadth below that process: 

 its greatest extent is in the transverse direction, 

 and it forms an angle salient posteriorly and 



