68 PRACTICAL PHYSIOLOGY 



preparation, keep the muscle and lower half of the nerve just moist 

 with tap-water saline, but allow the upper half of the nerve to dry. 

 As the nerve begins to dry, irregular contractions of the muscle come 

 on which are stopped by moistening the nerve ; showing that loss of 

 water acts as a stimulus to nerve. If the drying is allowed to continue, 

 the dry portion loses its irritability and dies. 



Now place upon the muscle a few crystals of NaCl; irregular con- 

 tractions will soon appear. These are partly due to the abstraction 

 of water, but also, as we shall see in the next experiments, to the 

 stimulatory effect of NaCl. 



The above experiments show that, in order to keep muscles and 

 nerves irritable and in good condition, they must be moistened with 

 a fluid which will neither give up nor abstract water from the tissue, 

 i.e. which is isotonic with the animal's lymph. For this purpose a 

 7 per cent, solution of NaCl in distilled water has frequently been 

 used. This solution, although isotonic with frog's blood, does not 

 contain the calcium and potassium salts found in blood-plasma and 

 lymph; and the question arises whether this alteration of the ions 

 in solution affects in any way the properties of muscle. 



In order to investigate this point, prepare two sartorius preparations 

 with their bony attachments and without injury to their muscular 

 fibres. Place one muscle in Biedermann's solution (-5 grms. NaCl, 

 2 grms. Na 2 HP0 4 , '2-04 grms. Na 2 C0 3 in 100 c.c. distilled water), 

 and the other in ? per cent. NaCl in distilled water. 



The muscle in Biedermann's solution, especially if the solution be 

 cool (3 10 C.), will after a shorter or longer interval begin to show 

 fibrillary twitches and may even contract regularly and rhythmically 

 as a whole. As soon as the result has been obtained, transfer the 

 muscle to a solution made by adding to 100 c.c. of *7 per cent. NaCl 

 solution in distilled water, 10 c.c. of a saturated solution of CaS0 4 , 

 or of a 10 per cent, solution of CaCl 2 in distilled water. The 

 spontaneous contractions will soon cease. 



The other muscle placed in the pure NaCl solution may remain 

 quiescent; very often it will show fibrillary twitchings and irregular 

 contractions, which are rapidly stopped by transferring the muscle 

 to the solution containing a calcium salt as well as NaCl. Should the 

 muscle, however, remain perfectly quiescent 1 it can still be shown 

 that it is no longer in a perfectly normal condition. After it has 

 remained in the solution for half an hour, remove it and connect it 



1 Frog's muscle differs somewhat in its behaviour in any given solution accord- 

 ing to the time of year, there being a marked difference between muscle in the 

 autumn and spring. 



