ii CHANGE OF FORM IN MUSCLE DURING ACTIVITY 105 



contracting in salted muscle, and found at the same time that it was 

 entirely abolished by adding one part CaCL to 5000 parts of the 

 NaCl solution. Locke also observed that the high tetanic con- 

 tractions described above disappeared after a short time, if the 

 muscle giving this reaction was thrown into NaCl solution, phis a 

 10 / Q saturated solution of CaS0 4 . Here it would seem that 

 a 0*6 / Q NaCl solution containing a calcium salt in the right 

 proportion is more "physiological" than a pure unmixed solution. 

 NaCl solutions whose percentage is over or under 0'5 pro- 

 duce much more marked changes in the reactions of striated 

 (frog's) muscle. In the first case, as Carslaw (68) found on 

 circulating the fluid through the vessels of the posterior end of 

 a frog, spontaneous excitation phenomena (tetanic contractions) 

 appear very quickly, and last for several minutes, with inter- 

 vening pauses. Solutions above 0*7 to 1 % NaCl produce, 

 moreover, a shortening of the muscle, which resembles contracture, 

 gradually increasing and diminishing again subsequently, while 

 at 2 % the fibrillar twitches cease, and only a slowly increasing 

 crenation, with corresponding loss of excitability, appears in the 

 muscle. Previous to this point, single as well as tetanic shocks 

 are accompanied by contracture. We may therefore say that 

 within certain limits of concentration the excitability of striated 

 voluntary muscle is considerably heightened, or directly stimulated 

 (chemically), by NaCl solutions, while at the same time a marked 

 inclination to contracture is present. 



This increase of excitability, and excitatory action of pure 

 NaCl solution, are greatly increased by the addition of certain other 

 salts of sodium, in particular of Na 2 C0 3 . An uninjured frog's 

 sartorius may be slightly excited when it is dipped into pure 

 0*6 / o NaCl solution, as indicated by fibrillar twitches, but these 

 are never of long duration. If, however, sodium phosphate 

 (Na 2 HP0 4 ) and a small quantity of Na 2 C0 3 are added to the 

 solution (5 grs. NaCl, 2 grs. Na 2 HPO 4 , and d'4-0'5 grs. Na 2 C0 3 

 to a litre of distilled water) it will almost invariably be found 

 that the immersed muscle, after a shorter or longer period of 

 rest, sets up rhythmical activity, provided the temperature be not 

 too high (3-10C.) (69). In most cases this is first exhibited 

 in a quick succession of weak, insignificant, and localised con- 

 tractions, discharged at the same height from a greater or less 

 number of primitive fibres. At times these movements are so 



