548 EDWARD B. MEIGS 



the physical relations between sarcostyles and sarcoplasm are in 

 general similar to those which obtain between a piece of gelatin 

 and a surrounding watery solution in which it is immersed. 



The striated muscle fibers are separated from each other by 

 spaces filled with lymph. The osmotic pressure of the salts of 

 the lymph is opposed within the muscle fibers by that of diffusible 

 potassium phosphate in solution in the sarcoplasm. The muscle 

 fibers contain a certain amount of water which is combined with 

 colloids and cannot act as a solvent for salts. A large proportion, 

 if not all, of this organic water is probably contained in the sar- 

 costyles. 



Stimulation of the muscle causes it to produce lactic acid. The 

 presence of the acid brings about a tendency for the sarcostyles 

 to swell at the expense of the sarcoplasmic spaces, and the shorten- 

 ing of the muscle fiber is the direct mechanical result of the in- 

 crease in the volume of its sarcostyles. Relaxation of the muscle 

 rnay be brought about by the combination of the lactic acid with 

 the K2HPO4 contained in the muscle fibers, and its consequent 

 neutralization. 



Smooth muscle consists of fibers which have an internal homo- 

 geneous structure and are not surrounded by semi-permeable 

 membranes. The smooth muscle fibers are separated from each 

 other by spaces containing lymph, and the physical relations 

 between the lymph and the smooth muscle fibers are generally 

 similar to those which obtain between the sarcostyles and the 

 sarcoplasm. 



The smooth muscle fibers contain a larger proportion of organic 

 water than the striated ones, and the remaining inorganic water 

 contains NaCl in the same concentration as that in which it 

 exists in the lymph. The tendency of the fibers to swell or to lose 

 fluid is dependent among other things on the concentration of 

 NaCl contained in the inorganic water. 



Stimulation of the smooth muscle causes it to produce lactic 

 acid, but in very much smaller quantity than is produced under 

 similar circumstances by striated muscle. The presence of small 

 quantities of the acid in smooth muscle brings about a tendency 

 for its fibers to give up fluid to the intervening lymph spaces, and 



