GENERAL PHYSIOLOGY OF MUSCLE-TISSUE 83 



phase atterminal the wrist became positive and the current passed in the 

 muscle toward its termination; and in the second abterminal it became 

 negative and the current now passed in the reverse direction. The action 

 currents which are observed in the frog's muscle were thus shown to be 

 present in the living human muscle, with this difference, however: that the 

 second phase abterminal instead of being weaker in man, is equally 

 strong with the atterminal. This experiment also revealed the fact that the 

 rapidity of propagation of the excitation wave was much greater in man, 

 amounting to about twelve meters per second. Hermann therefore denies 

 the pre-existence of electric currents and regards them as due to localized 

 temporary disintegration of the muscle in consequence of activity, as they 

 disappear on the restoration of the muscle to its normal condition. 



SPECIAL ACTION OF MUSCLE GROUPS 



The individual muscles of the axial and appendicular portions of the 

 body are named with reference to their shape, action, structure, etc.; e.g., 

 deltoid, flexor, penniform, etc. In different localities a group of muscles 

 having a common function is named in accordance with the kind of motion 

 it produces or to which it gives rise: e.g., groups of muscles which alternately 

 diminish or increase the angular distance between two bones are known 

 respectively as flexors and extensors; such muscle groups are usually found 

 in association with ginglymus joints. Muscles which rotate the bone to 

 which they are attached around its own axis without producing any great 

 change of position are known as rotators, and are found in association with 

 enarthrodial or ball-and-socket joints. Muscles which impart an angular 

 movement to the extremities to and from the median line of the body are 

 termed adductors and abductors respectively. 



In addition to the actions of individual groups of muscles in producing 

 special movements, in some regions of the body, several groups of muscles 

 are coordinated for the accomplishment of certain 

 definite functions; e.g., the functions of respiration, 



mastication, etc. The coordination of axial and * 



appendicutar muscles enables the individual to as- 

 sume certain postures, such as standing, sitting, and F 

 lying; to engage in various acts of locomotion, as A W 

 walking, running, dancing, swimming. I 



Levers. The function or special mode of action w"~ p A*' 



of individual muscles can be understood only when FlG 39 _ THE THREE OR- 

 the bones with which they are connected are regarded DERS OF LEVERS. 

 as levers whose fulcra or fixed points lie in the joints 



where the movement takes place, and the muscles as sources of power for 

 imparting movement to the levers with the object of overcoming resistance. 



In mechanics levers of three kinds or orders are recognized according 

 to the relative positions of the fulcrum or axis of motion, the applied 

 power, and the weight to be moved. (See Fig. 39.) 



In levers of the first order the fulcrum, F, lies between the weight or 

 resistance, W, and the power or moving force, P. The distance P F is 

 known as the power arm and the distance W F as the weight arm. As 

 examples of this form of lever found in the human body may be mentioned : 



