ACTION OF FORCES ON ORGANISMS. S3 



motions and exercise of young animals as one of 

 the causes of their development. In a young mam- 

 mal, if compelled to live without motion, there 

 would undoubtedly be a lack of muscular and ner- 

 vous development ; also there would be a most im- 

 perfect circulation of the blood, causing a host of 

 effects which would stunt the growth and eventu- 

 ally probably kill the animal. The cruelty of the 

 experiment has probably prevented its ever being 

 tried, but the evidence of this sort to be found 

 among the human race is only too convincing. 

 Every animal has a limited number of methods of 

 motion and exercise which are demanded by any 

 normal environment. This limited number of mo- 

 tions must influence the development of the ani- 

 mal in certain definite directions, favouring some 

 points of growth more than others ; just as many 

 forces acting in various directions on a body resolve 

 themselves into one single resultant direction of 

 force along which the body moves. 



The records of pathology are full of evidence 

 showing the effects of abnormal forces upon the 

 tissues of the human body. Almost all diseased 

 growths of tissues may be traced as resulting from 

 some change in the normal forces acting on the 

 tissues, or to the introduction of a totally new 

 force or stimulus. The change of a living surface 



