M 4- 



STRIATED MUSCLE 87 



sects, for instance, where a band of anisotropic areas in the fibrils extends 

 through the middle of the j area. When found, this band is called the 

 N band (Fig. 84). Its presence causes some unimportant complications 

 in the contraction processes. The isotropic bands are designated by 

 small letters. 



In most muscles the bands are so fine and close set that it is difficult 

 to distinguish them clearly. Then, again, one does not know which stage 

 of contraction is presented. The usual con- 

 dition shows one of the intermediate stages, 

 as in the sucker muscle, where the eye of 

 the ordinary observer would take each of 

 the two ends of the divided Q stripe for the 

 Q stripe of a resting muscle, until study 

 showed the true relations. 



Some sure way of fixing a bit of muscle 

 so that it will be certainly either relaxed or 

 contracted would be a useful method. A 

 muscle fixed under pressure or relaxed does 

 not necessarily show its fibrils in either 

 condition. The hardest thing to get is a 

 fiber in which there is a slow contraction 

 wave showing as in Figure 83. Many sud- 

 den and contorted changes that are almost 

 useless for study are usually found in crus- 

 tacean muscle fixed in the ordinary reagents. 



Technic. The element of "luck" ap- 

 pears to be a large one in the preparation 

 of striated muscle tissue. The best histo- 



logical methods, when most carefully carried out, are pretty sure to give 

 bad results from the point of view of him who wishes to study the stages 

 and processes of contraction. An even more careful study, than has 

 been made of the conditions under which muscle may be killed so as 

 to show any particular stage, is most desirable. Muscle which has been 

 allowed to die a natural death and which has been killed with chloro- 

 form and in many other ways should be examined. Animals should be 

 killed with poisons of marked muscular reactions and the condition of 

 this tissue noted. The tissue can also be studied, to a certain extent, 

 while it is yet alive. 



LITERATURE 



FIG. 84. Bit of muscle fiber from 

 the body-wall of an adult larva 

 of Corydalis cornutis. Shows the 

 (N) stripe near the Krause's 

 membrane (Z). nd., nucleus. 



The works of Rollet, Engelmann, Retzius, and others should be read by those who 

 wish to go further into the subject. 



