PHYSIOLOGY OF SMOOTH AND STRIATED MUSCLE 533 



do this by simple inspection of the piece of muscle, for the propor- 

 tional change of length undergone by smooth muscle fibers is very 

 considerable. I was careful, however, to make my judgments of 

 the changes in length as objective as possible. Where the behav- 

 ior of a single piece of tissue was being studied, the question 

 whether the fibers had shortened or lengthened much or little 

 was in each case decided before weighing. It was found that the 

 amount of change in weight could in most cases, be predicted sur- 

 prisingly accurately from a knowledge of the change which had 

 taken place in the length of the muscle fibers. In many cases 

 the changes undergone by two pieces of muscle, of which the 

 fibers had about the same length at the start, were compared 

 with each other. In a few cases, the length of the fibers of pieces 

 of muscle was measured at various stages of the experiment. 



It has been found to be a very general rule that increase in 

 the weight of a piece of smooth muscle goes hand in hand with 

 increase in the length of its fibers, while decrease in the weight of 

 the muscle is accompanied by a decrease in the length of its fibers. 

 For the evidence on this point, the reader is referred to the series 

 of protocols of the experiments. Some of the cases are very strik- 

 ing. Pieces of smooth muscle, transferred from Ringer to half 

 strength Ringer, for instance, gain weight and lengthen slowly; 

 while pieces of smooth muscle, transferred from Ringer to double 

 strength Ringer, lose weight and shorten rapidly (Experiments 

 33, 52, 55 and 57). 



In isotonic NaCl and KCl solutions, smooth muscle undergoes 

 a diphasic change of weight. In the NaCl solution it first gains 

 weight and then loses, while in the KCl solution it first loses 

 weight and then gains. In both cases increase in weight tends to 

 be accompanied by lengthening of the muscle fibers and decrease 

 in weight by shortening (Experiments 34, 35, 65 and 73). It will 

 be noted that in these experiments the changes in weight and 

 length do not run exactly parallel. In the NaCl solution the 

 muscle begins to shorten a good while before it begins to lose 

 weight, while in the KCl solution, it remains shortened for some 

 time after it has begun to gain weight. These results are, how- 

 ever, just what should be expected on the supposition that an 



