106 PRACTICAL PHYSIOLOGY 



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 prepara- 

 tions 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 HPO 4 , 2-04 grms. Na 2 C0 3 in 100 c.c. 

 distilled water), and the other in -7 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 CaSO 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 

 to a myograph lever and stimulate it with a single maximal break 

 shock. The contraction recorded on the drum will be no longer an 

 ordinary single contraction, but a series of tetanic twitches of 

 abnormal height and duration. Now remove the muscle, immerse 

 it for ten minutes in the solution containing the added calcium salt, 

 and again record its response to the same stimulus. A normal single 

 contraction will be obtained. It is clear that sodium salts, when 

 acting alone on skeletal muscle, have a powerful stimulatory effect, 

 and that this can be neutralised by adding a certain proportion of 

 calcium salt. For this reason " normal " saline solution is always 

 made with tap-water instead of with distilled water. Some tap- 

 waters, however, do not contain nearly enough calcium to bring 

 about complete neutralisation of the sodium salt. 



From the above experiments we learn certain facts of considerable 

 practical importance. We see that tissues are greatly affected by 

 changes in the osmotic pressure of the fluid surrounding them. Care 

 must therefore be taken not to expose the tissues of an animal or 

 man to fluids which are not isotonic with the blood-plasma. In 

 man the solution of NaCl isotonic with the blood-plasma is only 

 just under 1 per cent., and therefore differs widely in strength from 

 the solution for a frog ; it is very necessary to bear this in mind 

 when injecting fluid into veins or under the skin, and when irrigating 

 the peritoneal cavity during operations. The saline solution tends 

 to leak through the walls of the blood vessels ; to prevent this 



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

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

 in the autumn and spring. 



