108 AX AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



kinds of muscle-tissue iu the different muscles of the same animal; the same 

 may be said of contractility. Although irritability, conductivity, and contrac- 

 tility are to be regarded as different properties of muscle protoplasm, they are 

 usually found to be developed to a corresponding degree in each muscle. 

 Those forms of muscle which require for their excitation irritants of slow and 

 prolonged action, are found to conduct slowly and to make slow and long- 

 drawn-out contractions, and muscles which are excited by irritants acting 

 rapidly and briefly are noted for the quickness with which they contract 

 and relax. 



Differences in the activity of the contraction process are made evident 

 by the duration of single contractions of different forms of muscle-tissue. 

 The duration of the contraction of the striated muscles of different animals 

 differs greatly, e. g. of the frog -^ second, of the turtle 1 second, of certain 

 insects only -^-^ second. Even muscles of apparently the same kind in the 



Pectoralia major 

 Omuli yoid //\^\~~~~~'j racUis ^^~~-^^ 



J • • • • I I 



Fig. 41.— Records of maximal isotonic contractions of four different muscles from a turtle, each 

 weighted with 30 grams : Pectoralis major ; omohyoid ; gracilis ; palmaris. The dots mark & second, and 

 the longer marks seconds (after Cash). 2 



same animal exhibit different degrees of activity. Cash 1 reports the following 

 differences in the duration of the contractions of different striated muscles of 

 a frog in fractions of a second: Hyoglossus, 0.205; rectus abdominis, 0.170; 

 gastrocnemius, 0.120 j semimembranosus, 0.108 ; triceps femoris, 0.104. Sim- 

 ilar differences are found to exist between different muscles in other animals 

 — in the turtle, for instance, as is shown by the myograms in Fig. 41. 



It is interesting to connect the rate of the contraction process in different 

 muscles with their function. The omohyoid muscle of the turtle is capable of 

 comparatively rapid contractions, and the action of this muscle is to draw back 

 the head beneath the projecting shell ; the pectoralis, on the other hand, 

 although strong, contracts slowly; it is a muscle of locomotion and has to 

 move the heavy body of the animal. Unstriated muscles, which are remark- 

 able for the slowness and the duration of their contractions, are found chiefly 

 in the walls of the intestines, blood-vessels, etc., which require to remain in a 

 state of continued contraction for considerable periods and do not need to alter 

 rapidly. It is the business of the heart-muscle to drive fluids often against 

 considerable resistance, and a strong, not too rapid, slightly prolonged contrac- 

 tion, such as is peculiar to it, would be best adapted to its function. The bulk 

 of the muscles of the bodies of warm-blooded animals arc capable of rapid 

 contraction and relaxation, but the rate normal to the muscle is found to vary 

 with the form of work to be done. The muscles which control the vocal 

 organs, for instance, have a very rapid rate of relaxation as w^ell as of con- 



1 Arrhivfiir Anatomie und Physiologie, 1880, Suppl. Bd., S. 147. ' Op. cit., S. 157. 



