ORIGIN OF DISEASE AN'D THE GERM THEORY. 147 



Again, it seems very possible that the comparative frequency 

 of hair-bearing cysts in the brain and in the ovaries points to 

 the original development of those structures. 



In turning now to a consideration of the erect posture, we find 

 many points of supreme interest and value bearing upon our 

 topic. 



Before it can stand erect, the newly-horn bahe is only capahle 

 of crawling as a means of progression, and for some time after 

 its birth the relation of its head and legs to its trunk is similar 

 to that presented by a lower animal. At a comparatively early 

 age the child begins to hear with all its weight upon its legs, and 

 this fact serves in some degree to explain the greater frequency 

 of knock-knee and bowed leg in human beings as compared with 

 animals. Among vertebrates the erect posture is maintained in 

 the more highly differentiated, and it may be supposed that 

 remote progenitors of animals which are now erect were prone. 

 It is clear that the lower surface of a prone animal corresponds to 

 the front surface of an erect animal. The ventral or abdominal 

 surface, which in a prone animal is in relation with the earth, 

 comes to he, in the case of an erect animal, in relation with 

 space. Herein a great alteration in the supply and loss of heat 

 is involved. To the prone the earth affords a protection from 

 excessive radiation. This is illustrated by the fact that rabhits, 

 when placed in the supine position, die of refrigeration. 



Again, it is manifest that the abdominal contents of an erect 

 animal tend, in case their supporting tissues should yield, to 

 press upon the pelvic and inguinal structures, while it is equally 

 clear that in prone animals the pressure is directed downwards 

 and also perhaps forwards, in accordance with the slope of the 

 ventral wall of the abdomen. Hence the fact that femoral, 

 scrotal, and obturator, herniee, are rare in animals as compared 

 with man, while diaphragmatic and umbilical herniee are equally 

 common, if not even more so. 



The rudimentary condition of the vertebrse of the tail — 

 coming as they do after those called sacral, which support the 

 pelvic girdle — has apparently special reference to the erect pos- 



Iture. There is no doubt that a bulky tail, or even a small one, 

 could not but embarrass the action of the legs of an erect 

 animal. Many arboreal animals assume the erect posture, and 

 yet possess tails ; but in them the tail is used as a prehensile 

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