320 OF THE PRIMARY TISSUES OF THE HUMAN BODY. 



fibres, some contracting whilst others are relaxing, and vice versti. It is difficult 

 to speak with confidence, however, in regard to the condition of the individual 

 fibres of a muscle, that is thrown into a state of continued spasmodic contraction ; 

 such as that produced by the application of the electric current to the centre of 

 its motor nerves ( 317). A state of this kind is often of considerable duration. 

 Thus the Author has known a case of Hysteric Trismus, in which the jaws 

 remained closed with the greatest firmness during five days. Whether the 

 individual fibres, in such instances, maintain a state of contraction without inter- 

 mission, or whether the contraction of the entire muscle is kept up by a con- 

 tinual interchange of the fibres actually engaged, is a very curious subject for 

 inquiry. 



319. Muscles do not lose their Irritability immediately on the general death 

 of the system, which must be considered as taking place when the circulation 

 ceases without a power of renewal ; in cold-blooded animals it is retained much 

 longer after this period than in the higher Vertebrata, in some of which it dis- 

 appears within an hour. The muscles of young animals generally retain their 

 irritability for a longer time than those of adults; on the other hand, those of 

 Birds lose their irritability sooner than those of Mammalia. Hence, as a general 

 rule, the duration of the irritability is inversely as the amount of respiration. 

 From experiments on the bodies of executed criminals, who were previously in 

 good health, Nysten ascertained that, in the Human subject, the irritability of 

 the several muscular structures departs in the following time and order : The 

 left ventricle of the heart first; the intestinal canal at the end of forty-five or 

 fifty-five minutes ; the urinary bladder nearly at the same time ; the right ven- 

 tricle after the lapse of an hour; the oesophagus at the expiration of an hour 

 and a half; the iris a quarter of an hour later; the muscles of Animal life 

 somewhat later; and lastly, the auricles of the heart, especially the right, which 

 in one instance contracted under the influence of galvanism sixteen and a half 

 hours after death. Itwill be presently shown that the departure of the irritability 

 is entirely dependent upon the cessation of the circulation; and that it may be pre- 

 vented from disappearing, and may even be recalled after it has ceased to manifest 

 itself, by transmitting a current of arterial blood through the muscles ( 323). 



320. Muscular Irritability is deadened by many substances, especially by 

 those which have a narcotic or sedative action on the Nervous system. In car- 

 bonic acid gas, hydrogen, carbonic oxide, or sulphurous acid gas, muscles con- 

 tract very feebly, or not at all, when stimulated; whilst in oxygen they retain 

 their irritability longer than usual. Narcotic substances, such as a watery solu- 

 tion of opium, when applied directly to the muscles, have an immediate and 

 powerful effect in diminishing or even destroying their irritability ; this effect 

 is also produced, though in a less powerful degree, by injecting these substances 

 into the blood. In the same manner, venous blood, charged with carbonic acid, 

 and deficient in oxygen, has the effect of a poison upon muscles; diminishing 

 their irritability, when it continues to circulate through them, to such a degree, 

 that they sometimes lose it almost as soon as the circulation ceases, as is seen in 

 those who have died from gradual and therefore prolonged Asphyxia. The un- 

 favorable influence of venous blood is also shown in the Morbus Creruleus ; 

 patients affected with which are incapable of any considerable muscular exertion. 

 Although most of the stimuli which occasion the contraction of muscles, when 

 directly applied to their fibres, operate also when applied to their motor nerves, 

 the same does not hold good in regard to those agents which diminish irrita- 

 bility. It is a fact of some importance, in relation to the disputed question of 

 the connection of muscular irritability with the nervous system, that when, 

 by the application of narcotic substances to the Nerves, their vital proper- 

 ties are destroyed, the irritability of the Muscle may remain for some time 

 longer; showing that the latter must be independent of the former. This was 



