GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 59 



beating for more than forty-eight hours in a solution containing Nad, CaCl, 

 and KC1, even when there are no energy-giving substances present in the 

 fluid. Howell ' says that NaCl is needed in the proportion in which it occurs 

 in the blood, to preserve the osmotic relations of the tissues, while Ca and Iv 

 are essential to the development of the rhythmic movements of the heart- 

 muscle. Loeb 2 made a careful study of the relation of salts of the blood to 

 the activity of striated and non-striated muscles. He found, as others had 

 done before, that a striated muscle if left in 0.7 per cent. NaCl solution in 

 time develops more or less rhythmic automatic contractions. He considers 

 that Xa, Ca, and K are held in the muscle, not only as salts, but in combi- 

 nation with the proteids, and that all of these are necessary to the normal 

 functional activity of the protoplasm. A fluid to deserve the name of physio- 

 logical must contain all these ions. The muscle contracts rhythmically in a 

 solution of pure NaCl because the Na drives some of the Ca and K out of 

 their ion-proteid combinations. If Ca and K are present in the solution, 

 this cannot occur. He goes so far as to say that were it not for the Ca and 

 K in the blood, the human skeletal muscles would show rhythmic contraction. 



A truly physiological solution would contain all the constituents of the 

 fluid of the blood, and a physiological salt solution would contain all the salts 

 of the blood, in the proportion in which they exist in the blood. The salts 

 would appear to have a twofold function : they would maintain the normal 

 imbibition relations of the cells, and they woidd supply the Xa, Ca, and K 

 ions which are required for the ion-proteid compounds in the muscle. The 

 quantities of inorganic salts are different in different tissues of the same 

 animal, which shows that the presence of these inorganic substances is 

 dependent not merely on the amount presented to them by the fluids in 

 which they arc bathed, but also on the chemical conditions within the cells, 

 each type of cell requiring a definite supply for its normal functional activity. 

 Howell reports a fact of interest in this connection : the muscle of the ven- 

 tricle of the heart of the terrapin does not make automatic rhythmic move- 

 ments in a Ringer's solution containing Xa, Ca, and K in amounts equal to 

 those occurring in the blood, but the large veins at the base of the heart do 

 make such contractions and supply the excitation necessary to rhythmic con- 

 traction of the whole heart. 



The presence of inorganic salts is essential to the normal functional 

 activity of nerves, as it is of muscles. If the nerve be subjected to distilled 

 water, it gradually loses its salts through osmosis, and imbibes water, and 

 the resulting chemical and physical change in its constitution is accompanied 

 by a loss of irritability. Likewise the withdrawal of water from a motor 

 nerve by drying, or by strong solutions of urea, glycerin, etc., causes a change 

 of irritability. The irritability is first increased, due to a concentration of 

 the salts within the nerve and to the mechanical excitation resulting from 

 the shrinkage of the tissue. W the change is a rapid one, it is frequently 

 accompanied by an active irritation, and the muscle connected with the nerve 



1 American Journal of Physiology, 1898, ii. |» 17. 2 Ibid., 1900, i i i . p. 383. 



