342 Dr. B. Ward Bichardson on Muscular [May 29, 



may perform its office under two distinct degrees of tension or pressure — 

 a low tension, in which the organ itself is reduced in size and moves 

 almost insensibly ; and a full tension, in which it is of larger size and 

 moves with a sufficient power to impel the blood so as to overcome the 

 arterial elasticity and the capillary resistance. 



Another fact bearing on this subject is, that in rapid decline of muscular 

 irritability the muscles most concerned in the support of the organic 

 functions, namely the heart and the muscles of respiration, are the last to 

 yield up their spontaneous power ; but when they have lost their power, 

 they are the last to regain it. To this rule there is one exception, viz. in 

 the muscular fibre of the right auricle of the heart. 



The author then explained that the degree of cold which suspends 

 irritability is fixed within certain measures of degree, from 38° to 28° F. 

 being the most favourable degrees of cold. Above a temperature of 

 38° .Fahr. the muscles in a little time pass into permanent rigidity, rigor 

 mortis. Below 28° the muscles, if the effect of the cold be extended to 

 their whole structure, pass into some new molecular condition from which 

 they do not return into active life, at least they do not by means of any 

 process of recovery of which we are at present conversant. 



Effect of Motor Forces. 



Cold, by the inertia it induces, suspends, under certain conditions, but 

 does not destroy, muscular irritability. The motor forces, on the contrary, 

 quicken the irritability for a brief period, and then completely destroy it. 

 A method may perhaps be discovered for overcoming the effects of these 

 forces, but at present it is not known. The mode in which all the 

 motor forces act in arresting irritability is by the induction of a con- 

 tractile state, which, once established, remains permanent. It should be 

 remarked, however, that the forces respectively named mechanical, 

 calorific, electrical, act with different degrees of intensity, perhaps because 

 we cannot as yet apply them, in this particular research, with equal 

 measures of intensity. The author here related his experiments on the 

 effect of the different forces upon the right auricle of the heart, and re- 

 ported as the result of his observations that, while all the forces act 

 ultimately alike in producing permanent contraction, the mechanical ex- 

 citation is much slower than the calorific; while electrical excitation 

 appears to hold an intermediate place, as if it were a combination of 

 mere mechanical motion with an increased temperature. Electrical tension 

 may nevertheless be increased so as to rival heat in its immediate effect 

 on contraction. 



The author here traced out the results of a series of short sharp 

 irritations of muscle with a needle-point, and compared them with the 

 effect of a blow, showing that in each case rigidity follows, but is much 

 slower in development when it is excited by the needle. 



The influence of heat in destroying irritability, by its power of pro- 



