1887.] Caff ein and Theine upon Voluntary Muscle. 239 



variation is observed in the action of the alkaloids on the different 

 mnscles of the same frog. In the triceps the rigor is more rapidly 

 developed, and more extensive than in the gastrocnemins. In the 

 sartorins rigor commences soon, increases rapidly, lasts for some 

 honrs, and then relaxes. 



The addition of lactic acid to a solntion of theine or caffein causes 

 the rigor to appear sooner, develop more rapidly, and attain a 

 greater maximum. Potash retards and diminishes the action of theine 

 or caffeine. Gnanidine produces at first its characteristic clonic con- 

 tractions, but these pass off long before the rigor of caffeine or 

 theine begins, and the appearance of the rigor is postponed as com- 

 pared with the rigor of theine or caffein alone. On comparing the 

 effect of gnanidine with that of chloride of barinm, we found that in 

 the case of the guanidine the rigor was longer in occurring, and its 

 maximum was greater than that produced by barium salts. The 

 addition of chloride of calcium to the solution of theine quickens 

 rigor and makes it more extensive. One phenomenon which seems 

 deserving of attention is the rhythmic contraction of the muscle pro- 

 duced by theine. This rhythm is so slow that it would escape attention 

 unless a very low rate of speed were used in the recording appa- 

 ratus ; it is sometimes as slow as from three to about one contraction 

 per hour; it may continue for twenty hours. The rhythm is usually 

 produced by small doses of theine, which do not cause a marked rigor ; 

 it may, however, occur at the commencement of what develops into a 

 lasting rigor, or at the relaxation of a pseudo-rigor, by which we 

 mean a phenomenon which might also be termed tetanic relaxation. 

 The rhythm is more rapid at the commencement of its occurrence 

 and slower towards its termination; it may be as rapid as twenty 

 relaxations and contractions in an hour, or as slow as between one and 

 two in an hour. The total extent of contraction and relaxation is 

 very small, amounting to about one-fifth of a millimetre. At first the 

 contractions and relaxations are equal in duration, but afterwards the 

 relaxations become more rapid and the contractions slower. In one 

 instance we observed the remarkable phenomenon to which we have 

 given the name of pseudo-rigor ; in this experiment the application 

 of the theine was followed by slight relaxation of the muscle, to this 

 succeeded an equal contraction, and then followed great relaxation 

 below the normal, so great indeed that the negative curve below the 

 abscissa strongly resembled the positive curve of contraction due to 

 rigor in most other experiments.* 



* This phenomenon is difficult to explain, but it suggests the possibility of a 

 transverse as well as a longitudinal contraction in muscular fibre. — March 29, 1887. 



