PHYSIOLOGICAL PROPERTIES OF THE MUSCLES. 537 



exposed nerves be now galvanized, the muscles of the legs are thrown into contraction, 

 showing that the nervous irritability remains. Reflex movements in the posterior 

 extremities may also be produced by irritation of the parts above the ligature. These 

 experiments, most of which we have frequently repeated, taken in connection with the 

 observations of Longet, leave no doubt of the existence of an inherent and independent 

 irritability in the muscular tissue. Contractions of muscles, it is true, are normally 

 excited through the nervous system, and artificial stimulation of a motor or mixed nerve 

 is the most efficient method of producing the simultaneous action of all the fibres of a 

 muscle or of a set of muscles ; but galvanic, mechanical, or chemical irritation of the 

 muscles themselves will produce contraction, after the nervous irritability has been 

 abolished. 



The conditions under which muscular irritability exists are simply those of normal 

 nutrition of the muscular tissue. When the muscles have become profoundly affected 

 in their nutrition, as the result of section of the mixed nerves or after prolonged paraly- 

 sis, the irritability disappears and cannot be restored. The determination of the pres- 

 ence or absence of muscular contractility, in cases of paralysis, is one of the methods of 

 ascertaining whether treatment directed to the restoration of the nervous power will be 

 likely to be followed by favorable results. If the muscular irritability have entirely dis- 

 appeared, it is almost useless to attempt to restore the functions of the part. 



A great many experiments have been made with regard to the influence of the circu- 

 lation upon muscular irritability, chiefly with reference to the effects of tying large vessels. 

 Among the most recent are those of Longet. He tied the abdominal aorta in five dogs and 

 found that voluntary motion ceased in about a quarter of an hour, and that the muscular 

 irritability was extinct in two hours and a quarter. When the blood was restored, after 

 three or four hours, by removing the ligature, the irritability and finally voluntary move- 

 ment returned. These experiments show that the circulation of the blood is necessary 

 to the contractility of the muscles. Tying the vena cava did not affect the irritability of 

 the muscles. In dogs in which this experiment was performed, the lower extremities 

 preserved their contractility, and the voluntary movements were unaffected up to the 

 time of death, which took place in twenty-six hours. 



The relations of muscular irritability to the circulation have been farther illustrated, 

 in some very curious and interesting experiments, by Dr. Brown-Sequard. The first 

 observations were made upon two men executed by decapitation. Thirteen hours and 

 ten minutes after death, when the muscular irritability had entirely disappeared and was 

 succeeded by cadaveric rigidity, a quantity of fresh, defibrinated venous blood, from the 

 human subject, was injected into the arteries of one hand and was returned by the veins. 

 It was afterward reinjected several times during a period of thirty- five minutes. The 

 whole time occupied in the different injections was from ten to fifteen minutes. Ten 

 minutes after the last injection, and about fourteen hours after death, the irritability was 

 found to have returned, in a marked degree, in twelve muscles of the hand. There were 

 only two muscles out of the nineteen, in which the irritability could not be demonstrated. 

 Three hours after, the irritability still existed, but it disappeared a quarter of an hour 

 later. The second observation was essentially the same, except that defibrinated blood 

 from the dog was used, and the experiments were made upon the muscles of the arm. 

 The irritability was restored in ail of the muscles, and it persisted, the cadaveric rigidity 

 having disappeared, twenty hours after decapitation. These experiments are exceedingly 

 interesting, as showing the dependence of irritability upon certain of the processes 

 of nutrition, which are probably restored, though temporarily and imperfectly, by the 

 injection of fresh blood. They are also important in connection with the study of 

 cadaveric rigidity of muscles, a condition which follows the loss of their so-called vital 

 properties. The subject of cadaveric rigidity will be fully discussed as one of the phe- 

 nomena of death. 



