220 THE PHYSIOLOGY OF MUSCULAR WORK 



inside its mother's womb during the last months of pregnancy 

 These movements he has studied both by palpation and by a 

 graphic record ; they resemble the respiratory movements of a 

 newly born infant in their irregular rhythm and in periods of 

 waxing and waning. The criticism that such respiratory move- 

 ments would draw the amniotic fluid into the lungs is not a serious 

 one, for the movements are slight, and even if the fluid were drawn 

 further than the naso-pharynx it would be rapidly absorbed, and 

 being sterile and isotonic, would not injure the foetus. It would 

 appear, therefore, that all the muscles of the body are exercised 

 during foetal life for the work which they have to perform after 

 birth. It is impossible to say that muscular contraction appears 

 at any definite time. 



Great advances have been made in the study of muscular 

 movements in man and animals since the introduction of in- 

 stantaneous photography. Before that time too much stress had 

 been laid upon the anatomical aspect of muscular movements. 

 It is impossible to analyse movement in the living by an examina- 

 tion of the points of origin and insertion of the different muscles 

 acting upon the joints of dead subjects. Such imperfect know- 

 ledge could only be partly corrected by careful observation of 

 the natural movements ; for the eye is not able to follow the 

 real sequence of events ; the impression given to the observer is a 

 composite one of several movements. It is owing to this fact that 

 many instantaneous photographs of men and animals in motion 

 do not appear true to nature and are inartistic. The credit of 

 first analysing movements by relays of instantaneous photographs 

 is due to Muybridge ; his work has been greatly extended by 

 Marey and others. If such photographs are seen in rapid succs- 

 sion the observer receives the impression that the objects are in 

 motion ; this is due to the persistence of visual impressions, and 

 is the principle involved in the bioscope. 



Another method introduced for the analysis of movements is 

 the graphic one developed by Marey. It may be explained as an 

 extension of the simple method of footprints. A man skilled in 

 woodcraft can tell the nature and pace of an animal from its 

 spoor or footprints, and by the examination of the fossils of such 

 impressions geologists have been able to study the movements of 

 animals which became extinct before the time of man. 



It would be outside the scope of this article to pursue this 



