ON MUSCULAR IRRITABILITY. 169 



not, with Dr. Eadcliife, fall into the error of considering that muscle neces- 

 sarily passes into a state of contraction in the absence of an elongating force; 

 for experiment shows that the most perfectly relaxed state of muscle is com- 

 patible with the absence of every trace of irritabilitj'. 



I shall nowproceed to narrate several experiments in which the relation 

 which blood bears to muscular tissue is more fully displayed, and by which it 

 is made evident that the blood gives the poAver by which the elongated or, 

 relaxed state of muscle is maintained. 



Exp. 1. — A frog is moderately chloroformed; when removed from the 

 vapour, particular note is made that the limbs are perfectly flaccid or relaxed, 

 and that the heart is beating. The heart is now exposed and excised, and in 

 a few seconds or miautes, accorchng to the amount of chloroform imbibed by 

 the tissues, the Umbs ivill spontaneoushj extend and become rhjidhj tetanic. 



Another fi'og was slightly chloroformed, and the observation made that 

 the heart was still actiag, and that the whole of the muscles were quite 

 flaccid. The structures of one thigh Avere then cut through to the bone, so 

 as to sever all nervous and vascular connexions. The muscles of this limb 

 gradually commenced to contract, and in a fcAV minutes the leg and foot were 

 extended and the webs stretched out. The muscles of the other limb and 

 the trunk generally remained in a completely relaxed state. After the lapse 

 of some minutes I observed a tendency in the unmutilated hmb to extend, 

 and in the fore feet to approach the central line of the body, and to clasp, 

 as in tetanus of the male frog. Directing my attention to the heart, I 

 could not detect any pulsation, and I therefore removed the parietcs of the 

 chest ; the access of air reexcited the action of the heart, and very quickly 

 the muscles of the unmutilated limb and general trunk became again flaccid. 

 The heart again losing power, the condition of contraction a second time 

 came on, and gradually became more and more complete. On reexamining 

 this frog after the lapse of an hour, I found that the muscles had again 

 become flaccid— this time not only in the unmutilated limb, fore feet, and 

 muscles of the trimk, but also in the limb which, as far as its soft parts were 

 concerned, was completely amputated. Not the slightest trace of irritability, 

 however, was now detectable. Nothing could be plainer than the teaching 

 of this experiment. The muscular tissue was subjected to a dual influence :— 

 first, the chloroform tending to excite it to contract; secondly, the blood, 

 or certain of its elements, tending to maintain it in the relaxed or elongated 

 state ; and accordingly as one or other of these influences prevailcct, the 

 muscles became alternately contracted or relaxed. After the cessation of the 

 circulation the antagonism was feebly continued bctAvecn the evaporating 

 traces of the chloroform on the one hand, and the interstitial juices of the 

 muscle on the other, the balance of power being so nicely adjusted that the 

 interstitial nutrition Avas just capable of restoring the relaxed condition, but 

 incapable of conferring the slightest degree of irritability upon the muscles. 

 It is rarely that we obtain this exact balance of the influences ; for if the 

 amount of chloroform in the muscles is too large, the condition of permanent 

 contraction obtains ; and if too small, there are shght evidences of returning 

 irritability after the muscle has become elongated. 



Another satisfactory mode of exhibiting this function of the blood is to 

 compress the abdominal aorta of a frog, and, having ascertained by the 

 microscope that the circulation in the lower limbs is securely arrested, oil all 

 parts of the body, Avith the exception of one limb, expose this to the vapour 

 of chloroform, protecting as much as possible all other portions of the body 

 from its influence. This limb wiU after a time shoAV a disposition to con- 



