PHYSIOLOGY OF SMOOTH AND STRIATED MUSCLE 503 



order to explain certain experimental results which have been 

 obtained with striated muscle it has been necessary to suppose 

 that this tissue contains potassium and phosphorus in combina- 

 tions other than potassium phosphate and that a considerable 

 part of the water of the tissue exists as organic water, which does 

 not act as a solvent for salts. It has been pointed out by Meigs 

 and Ryan that the conditions in smooth muscle could be explained 

 without invoking the aid of semi-permeable membranes by apply- 

 ing to it the same suppositions in a somewhat extended form.^* 



It will be interesting, therefore, to have further evidence on the 

 "question whether the smooth muscle fibers are surrounded by 

 semi-permeable membranes, and a large part of this article will 

 be devoted to the presentation of such evidence. 



The chemistry and physics of the contraction of smooth muscle 



The author has already given evidence to show that the con- 

 traction of smooth muscle is the mechanical result of loss of fluid 

 by its fibers.^"* It has been found that the changes of weight 

 which occur in smooth muscle as the result of its immersion in 

 isotonic and non-isotonic solutions are seldom unaccompanied 

 by corresponding changes in the length of the muscle fibers. 

 These changes in length have been followed and recorded in the 

 same experiments in which the weight changes undergone by the 

 tissue have been studied, and they will be described and discussed 

 in the proper place. It may be said here, however, that it is a 

 very general rule that increase in the weight of the muscle is 

 accompanied by lengthening; and decrease in weight by shorten- 

 ing ; and this fact confirms the view that the contraction of the tis- 

 sue is under normal circumstances the mechanical' result of loss 

 of fluid by its fibers. Certain experiments will later be described 

 which suggest that the formation of lactic acid may play an 

 important part in the physiology of the contraction of smooth 

 muscle. 



i»Loe. cit., pp. 411-413. 



1* Meigs; American Jour. Physiol., 1908, vol. 22, p. 477; 1912, vol. 29, p. 317. 



