The Microscope. 229 



indrical or tapering, the deviation from the type is in all directions 

 and at all parts of the fiber. These statements are based upon 

 specimens subjected to reagents, as no determination of the form of 

 the fiber was attempted on fresh material. 



The measurement of the diameter of fibers ofPers serious diffi- 

 culties. Apparently the most simple method would be to measure 

 the sections of fibers, but this was abandoned owing to the incon- 

 stancy of the fascicules (see Part II.) and consequent difficulty in 

 tracing the individual fibers through a series of sections in order to 

 find where they are of full size. In isolated preparations, though it 

 is not so difficult to determine what part of a fiber to measure, there 

 are two sources of error. In the dissociating agents used, the fibers 

 shrink in length, and consequently increase in diameter, and though 

 the two diameters at a given point may be so different, as shown in 

 sections (Fig. 20), only one of them can ordinarily be measured. 

 The average diameter of twenty fibers from the vastus externus of 

 the mouse, in the fresh state, was 50 ^ — the largest and smallest 

 being 80 /^ and 30/"; the average of thirty fibers dissociated in caus- 

 tic potash and showing a decided shrinkage in length was 53 /", the 

 largest and smallest being 80/' and 30,"; the average of thirty fibers, 

 dissociated in nitric acid in situ, and having a shrinkage of one- 

 ninth their length, was 56 /', the largest and smallest being 100 f^ and 

 20/"; the average of thirty fibers dissociated in nitric acid, and hav- 

 ing a shrinkage of one-third in length was 70/", the largest and 

 smallest being 100 /" and 30 /'. In the other animals studied, the 

 average diameter of the fibers was considerably less. 



Tendinous ends were found varying from 20/" to 125/", and 

 intramuscular ends from 2 ," to 20 /", depending on the bluntness of 

 the end and the part measured . 



According to Rollett (1856) fibers which end within a muscle 

 are small in diameter throughout their whole length. He assumed 

 that they are developing fibers which do not yet reach from tendon 

 to tendon. In the mouse and sparrow this is clearly not the case, as 

 some fibers which extend from tendon to tendon are small and others 

 large, while some tapering fibers with intramuscular ends are large 

 (Fig. 12) and others small (Fig. 8). In the trapezius and the 

 abdominal muscles of the mouse, fibers which extend side by side 

 from tendon to tendon, show a great difference in size, one being 

 three or four times as large as another (Fig. 6 and 8, and also Fig. 

 47, PL XII in Part II). 



6. In the skin and mucosa so clear a determination of the 



