PHYSIOLOGICAL PROPEETIES OF THE MUSCLES. 533 



arrangement in this tissue is peculiar. From the smallest arterioles, capillary vessels are 

 given off, arranged in a net- work with tolerably regular, oblong, rectangular meshes, 

 their long diameter following the direction of the fibres. These envelop each primitive 

 fasciculus, enclosing it completely, the artery and vein being upon the same side. The 

 capillaries are smaller than in any other part of the vascular system. When distended 

 with blood they are from ^V^ to -^^ of an inch in diameter ; and when empty their 

 diameter is from -^V^ to inrViy f an inch. 



The arrangement of the lymphatics in the muscles has never been definitely ascer- 

 tained. There are numerous lymphatics surrounding the large vascular trunks of the 

 extremities and of the abdominal and thoracic walls, which, it would appear, must come 

 from the substance of the muscles ; but they have never been traced to their origin. 

 Sappey has succeeded in injecting lymphatics upon the surface of some of the larger 

 muscles, but he has not been able to follow them into the muscular substance. 



Connection of the Muscles with the Tendons. It is now generally admitted that the 

 primitive muscular fasciculi terminate in little conical extremities, which are received 

 into corresponding depressions in the bundles of fibres composing the tendons; but this 

 union is so close, that the muscle or the tendon may be ruptured without a separation at 

 the point of union. In the penniform muscles this arrangement is quite uniform and 

 elegant. In other muscles it is essentially the same, but the perimysium seems to be con- 

 tinuous with the loose areolar tissue enveloping the corresponding tendinous bundles. 



Chemical Composition of the Muscles. We are as yet so little acquainted with the 

 exact constitution of the nitrogenized constituents of the body, that we cannot appreciate 

 the nature of all the proximate principles that exist in the muscular substance. The 

 most important of these is musculine. This resembles fibrin, but it presents certain points 

 of difference in its behavior to reagents, by which it may be readily distinguished. One 

 of its peculiar properties is that it is dissolved at an ordinary temperature by a mixture 

 of one part of hydrochloric acid and ten of water. 



The muscular substance is permeated by a fluid, called the muscular juice, which con- 

 tains a peculiar coagulable principle called myosine. 



Combined with the organic principles, we find a great variety of mineral salts in the 

 muscular substance, that cannot be separated without incineration. Certain excremen- 

 titious matters have also been found in the muscles ; and probably nearly all of those 

 eliminated by the kidneys exist here, although they are taken up by the blood as fast as 

 they are produced and are consequently detected with difficulty. The muscles also con- 

 tain inosite, inosic acid, lactic acid, and certain other acids of fatty origin. During life, 

 the muscular fluid is slightly alkaline, but it becomes acid soon after death. The muscle 

 itself, during contraction, has an acid reaction. The muscular juice is alkaline or neutral 

 after moderate exercise, as well as during complete repose ; but, when a muscle is made 

 to undergo excessive exercise, the lactic acid exists in greater quantity, and the reaction 

 becomes acid. 



Physiological Properties of the Muscles. 



The general properties of the striated muscles, as distinguished from all other tissues 

 except the involuntary muscles, are as follows: 1. Elasticity; 2. Tonicity; 3. Sensi- 

 bility of a peculiar kind ; 4. Contractility, or irritability. These are all necessary to the 

 physiological action of the muscles. Their elasticity is brought into play in opposing 

 muscles or sets of muscles ; one set acting to move a part and to extend the antagonistic 

 muscles, which, by virtue of their elasticity, retract when the extending force is removed. 

 Their tonicity is an insensible and a more or less constant contraction, by which the 

 action of opposing muscles is balanced when both are in the condition of what we call 

 repose. Their sensibility is peculiar and is expressed chiefly in the sense of fatigue and 



