214 STRUCTURE AND ENDOWMENTS OF ANIMAL TISSUES. 



upon the vital condition of the system at the time of death. When it 

 has been weakened or depressed by previous disease, the irritability of 

 the muscles speedily departs ; and the stiffening comes on early, and 

 lasts but a short time. Thus, after death from Typhus, the limbs have 

 been sometimes known to stiffen within 15 or 20 minutes. On the other 

 hand, when the general vigour of the system has not been previously 

 impaired, and death has resulted from .some sudden cause, the irritability 

 of the muscles is of longer duration, and their stiffening is consequently 

 deferred. The commencement of the rigidity usually takes place within 

 seven hours after death ; but twenty or even thirty hours may elapse 

 before it shows itself. Its general duration is from twenty-four to 

 thirty-six hours ; but it may pass off much more rapidly, or it may be 

 prolonged through several days. It affects all the muscles composed of 

 the striated fibre with nearly the same intensity ; except that the flexors 

 usually contract more strongly than the extensors (as in sleep), the 

 fingers being closed upon the palm, the hand bending on the fore-arm, 

 and the lower jaw being drawn firmly against the upper. And it even 

 manifests itself in muscles that have been thrown out of use by paralysis, 

 provided that their nutrition has not been seriously impaired. 



368. This tonic contraction, however, is most remarkably manifested 

 in the non-striated fibre ; and especially in the heart and blood-vessels. 

 As soon as the muscular walls of the several cavities lose their irrita- 

 bility, they begin to contract forcibly upon their contents, and thus be- 

 come stiff and firm, although they were previously flaccid. In this 

 manner, the ventricles of the heart, which are the first parts to lose 

 their irritability, become rigid and contracted within an hour or two 

 after death ; and usually remain in that state for ten or twelve hours, 

 sometimes for twenty-four or thirty-six, then again becoming relaxed 

 and flaccid. This rigid contracted state of the heart, in which the walls 

 are thickened and the cavities diminished, was formerly supposed to be 

 a result of disease, and was termed concentric hypertrophy ; but it is 

 now known to be the natural condition of the organ, at the period when 

 the rigor mortis occurs in it. The contraction of the arterial tubes is 

 so great, as to produce for the time a great diminution in their calibre ; 

 and this doubtless contributes to the passage of the blood from the arte- 

 rial into the venous system, which almost invariably takes place within 

 a few hours after death. The arteries then enlarge again, and become 

 quite flaccid, their tubes being emptied of the previous contents ; and it 

 was from this circumstance, that the ancient physiologists were led to 

 imagine that the arteries are not destined to carry blood, but air. 



369. As soon as the Rigor Mortis departs, the -muscles pass into a 

 state^ of decomposition ; in fact, it is by the commencement of decom- 

 position, that the cessation of this vital property is occasioned. Thus 

 we may regard the Rigor ]\Jortis as the last act of the Muscular Con- 

 tractility : and in this respect it corresponds with the coagulation of the 

 blood, which also is the closing act of its life, when it is drawn from the 

 living body, or has ceased to circulate ( 184). There are, indeed, many 

 remarkable points of correspondence between the two phenomena ; which 

 have induced some physiologists to believe, that rigor mortis is in fact 

 nothing else than the coagulation of the blood in the muscles. It has 



