IRRITABILITY. 



The same confusion of ideas on the subject 

 of the activity of the animal and the irritability 

 of the muscular fibre prevails, I believe, 

 amongst our own physiologists ; at least, in 

 conversation with two, who may rank amongst 

 the first, I found that they had uniformly con- 

 sidered the respiration and the irritability to be 

 directly, instead of inversely, proportionate to 

 each other. 



That singular and interesting property of the 

 lower orders of animals termed tenacity of life 

 is, on the other hand, distinctly associated 

 with a high degree of irritability of the mus- 

 cular fibre. The property may be denned as 

 consisting of the power of sustaining the pri- 

 vation of respiration, the privation of food, 

 various mutilations, divisions, &c. It is greater 

 as we descend in the zoological scale. As 

 activity depends upon the presence and condi- 

 tion of the spino-cerebral masses acted upon 

 by arterial blood, tenacity of life depends upon 

 the diminution or absence of these masses and 

 of this highly artenalized blood, being greatest 

 of all in those animals which approach a mere 

 muscular structure. Almost the sole vital pro- 

 perty then remaining is the irritability; and 

 this property does not immediately sufier from 

 division. 



It is possible to reduce some of the reptile 

 tribes to a state approaching that of animals 

 still lower in the scale, by removing, by very 

 slow degrees, successive portions of the ner- 

 vous masses. This is most readily done in 

 animals in which the respiration is already low, 

 and the irritability high, as in the fetus, in the 

 very young animal, in the reptile, &c., as in 

 the experiments of Legallois,* M. Serres,f 

 myself,| &c. 



There is, even in animals most tenacious of 

 life, one kind of mutilation one kind of in- 

 jury not well borne. As the blood is in its 

 louest condition of stimulus, it cannot be 

 withdrawn with impunity ; even frogs soon 

 perish if their blood be allowed to flow. As the 

 irritability, on the other hand, is high, certain 

 stimuli, as galvanism, slightly elevated tem- 

 peratures, &c. are speedily fatal. The batra- 

 chia are promptly destroyed by immersion in 

 water of a temperature of 108 of Fahr., and 

 some fish and Crustacea perish in great num- 

 bers under the influence of a thunder-storm. 

 It is a singular fact, that the fish alone, whose 

 food is found amongst animals of a high irrita- 

 bility, should possess an electrical organ for 

 the destruction of its prey. 



The application of stimulus has uniformly a 

 tendency to reduce the degree of irritability. 

 The exclusion of all stimuli allows its augmen- 

 tation. During active exercise the irritability 

 is diminished ; during sleep it is proportionally 

 augmented. 



We are nowled to take anotherview of this sub- 

 ject of irritability. What is its source ? flow is it 

 renewed \\henithasbeenexhausted? Theseques- 

 tionslead us totakeupanotlierofgreatinterest,to 



* Experiences sur le Principe de la Vie. 



t AnatomieCompartie du Cerveau, tome ii.p. 224. 



J Essay on the Circulation, chap. iii. $ 1. 



physicians especially, viz. what is the condition 

 of the muscular irritability in those cases in 

 which the influence of the cerebrum, or of the 

 spinal marrow, orboth, isremoved respectively? 

 We cannot discuss this subject more clearly 

 than by adducing the following observations, 

 read before the Royal Medico-Cliirurgical 

 Society and published in its Transactions, in 

 the year 1839. 



The utmost discrepancy of opinion prevails 

 amongst physiologists and medical writers upon 

 this subject. Prochaska, Nysten, and Legallois 

 state, that the irritability of the muscular fibre 

 remains in paralytic limbs ; whilst Professor 

 Muller and Dr. Sticker assert the contrary. No 

 attempt has been made to reconcile a contra- 

 diction not very honourable to our science. To 

 explain this discrepancy of opinion is one of 

 the objects of this communication. 



The authors to whom I have referred, misled 

 by the generic term and idea of paralysis, have 

 not sufficiently distinguished between its dif- 

 ferent species. Yet it will be found, as we pro- 

 ceed, that this distinction is of the utmost im- 

 portance in the explanation of the phenomena. 

 In fact, cerebral paralysis, or that which re- 

 moves the influence of the brain, and spinal 

 paralysis, or that which removes the influence 

 of the spinal marrow, are in totally opposite 

 conditions in reference to the irritability of the 

 muscular fibre in the limbs severally affected ; 

 facts equally obvious in experiments and in 

 clinical observations. I must make quota- 

 tions of some length, for these are necessary to 

 show the present state of the science. I shall 

 then proceed to the detail of my own investi- 

 gations. 



The first distinct notice of this subject which 

 I think it necessary to adduce, is contained in 

 the following extract from the Opera Minora of 

 Prochaska:* " Vis nervosa quae in nervis a 

 commercio cum cerebro separatis superest, non 

 una alterave musculi contractione, quam irri- 

 tati cient, exhauritur, sed millenis plane con- 

 vulsionibus excitandis par est ; quod expertus 

 sum in rana, cui medullam spinalem in dorso 

 abscidi. Supervixit huic vulneri aliquot die- 

 bus; interim irritando medullae spinalis partem 

 earn, quoe erat infra sectionem, convulsiones in 

 artubus inferioribus excitavi toto tempore, quo 

 supervixit, plane mnumeras ; neque extremi- 

 tates inferiores prius mortuae sunt, quam tola 

 rana; Dein quod vis nervosa in nervis diu 

 persistere possit citra cerebri auxilium probare 

 videntur musculi paralytic!, in quorum nervis 

 ob compressionem aliquam pra-ternaturalem to- 

 tum commercium cum cerebro sublaturn est, 

 nihilominus tamen a stimulo electric.e scintilla 

 longo jam tempore paralytic! musculi convel- 

 luntur." 



More detailed remarks were made by Nysten, 

 and these, from being founded upon very dis- 

 tinct post-mostem experiments on the human 

 subject, have excited more attention. This ce- 

 lebrated physiologist observes, " Chez deux 

 apoplectiques qui avaient succombe au bout de 



* Ed. 1800, p. 84. 



