596 COMPARATIVE STUDY OF MOTION. 



a bicycle-rider is three and one-half minutes for each kilometer, or a rate of 4.73 

 meters a second, with a daily capability of from 90 to 100 kilometers. The normal 

 capability of a workman is in this connection assumed by comparison to be 6.3 

 kilogrammeters a second. A bicycle-rider, going at an average rate, traverses 

 the same distance in half the time and with half the expenditure of energy that 

 a pedestrian requires. With the same metabolic consumption of muscular tissue, 

 the exertion and the degree of fatigue are greater in walking than in cycling. 

 In long-continued cycling, likewise in long marches, there is an increase in the 

 consumption of energy for the successive units of distance covered; at a moderate 

 pace this increase amounts to about 20 per cent. 



The pressure on the ground in walking is distributed in the following manner: 

 The supporting leg always presses more firmly on the ground than the other; 

 the longer the step the stronger the pressure. The heel attains the maximum 

 pressure more rapidly than the point of the foot. 



The length of the step varies not inconsiderably even when a voluntary 

 attempt is made to have the steps of equal length ; as do also the degree of spread- 

 ing of the legs and the duration of the various phases of walking. 



Running (Fig. 202) differs from rapid walking in the fact that a mo- 

 ment exists in which both legs are off the ground, so that the body hovers 

 in the air. The active leg, in being forcibly extended from a more flexed 

 position, must each time give the body the necessary impetus. 



In jumping (Fig. 203) the body is suddenly raised by the most rapid 

 and powerful contraction possible of the muscles in the lower extremi- 

 ties, care being taken at the same time to maintain the equilibrium by 

 appropriate muscular action. 



Pathological. Variations in the walking movements depend primarily upon 

 diseases of the bones, joints, ligaments, muscles, and tendons. Then the motor 

 nerves must be taken into consideration, irritation and paralysis of which give 

 rise to disturbances of the normal movements. The extent to which the sensory 

 nerves and the reflex apparatus in the spinal cord influence the gait is pointed out 

 on pages 716 and 728. 



H. Vierordt has applied the graphic method to the analysis of pathological 

 varieties of gait. Among these are, for example, the spastic, the oscillating or 

 zig-zag gait, the gait of tabes and that of paralysis agitans. Abasia and astasia 

 are the terms applied by Blocq in 1888 to the inability to walk and stand, arising 

 from cerebral affections (hysteria, hypochondria, violent emotions, imperative 

 conceptions, vertigo), while all other movements, even those of the legs, can be 

 executed with full force and coordination. 



COMPARATIVE STUDY OF MOTION. 



The absolute muscular energy in animals is not, generally speaking, appreciably 

 different from that of man. The greater exhibitions of force encountered in the 

 animal kingdom arise from the thickness and number of the muscles, as well as 

 from differences in the arrangement of their leverage or in the means for the 

 transference of force. Thus, for example, insects are" capable of exerting a great 

 amount of force; some of them being able to drag 67 times their own weight, 

 while a horse can scarcely drag its own weight. While further, for example, a 

 man, by pressure on a dynamometer with one hand, overcomes a weight equal 

 to 0.70 time his own body-weight, a dog by lifting his lower jaw can overcome 

 a weight 8.3 times that of his body; a crab by closing its claw overcomes 28.5 

 times its weight; a mussel in closing its shell, 382 times its body-weight. 



Standing is made easier in quadrupeds by reason of the much greater sup- 

 porting surface; the springing animals assume, besides, more of a sitting position, 

 and often use the tail as an additional support (kangaroo, squirrel). Birds possess 

 a mechanical arrangement by means of which, in perching, their toes are flexed; 

 in this way they are able to retain their grasp on twigs when asleep. In the 

 stork and the crane, prolonged standing on one leg is made easy by the fact that 

 no muscular action is required to render the leg rigid; fixation is secured by a 

 process of the tibia fitting into a depression on the articular surface of the femur. 



In walking, a gait can be distinguished in quadrupeds ; the four feet are moved 



