270 Mr. H. G. Seeley on the Origin 



tually take place as we have theoretically found should take 

 place, and if they produce the results which theory assigns to 

 them, then the conviction which such phenomena will enforce 

 we may fortify by examples of abnormal growths, due to 

 mechanical causation, afforded by pathology, and test its truth 

 by application to morphology. 



In the first place, every organism on the earth's surface has 

 upon it the pressure of the earth's atmosphere — a pressure 

 which, in the case of a man's body, is usually computed at 

 about 70 to 100 tons ; and therefore growth can only take 

 place when a force is manifested which is sufficient to lift the 

 atmosphere and hold it up. The skin experiences this pres- 

 sure, and in consequence, probably, has its superficial epithe- 

 lial cells flattened to scales. The life is crushed out of them 

 by a pressure which is never appreciably relaxed, and they die 

 under it, and are removed. Such is an example of atrophy. 

 But when the skin is exposed to special extra intermittent 

 pressure, it grows. This relation of growth to pressure was 

 known to John Hunter, and is clearly expounded by him. 

 Generalizing from a consideration of corns, he remarks, in a 

 passage quoted by Sir James Paget : — " The cuticle admits 

 of being thickened from pressure in all parts of the body : 

 hence we find that on the soles of the feet of those who walk 

 much the cuticle becomes very thick ; also on the hands of 

 labouring men. We find this wherever there is pressure, as 

 on the elbow, upper part of the little toe, ball of the great 

 toe, &c." 



With regard to the internal organs, it would lead me too 

 far away from the object of this writing upon bones to discuss 

 the interrelations of them all. I therefore omit whatever can 

 be dispensed with, and limit myself to what is taught by a 

 few great sets of organs, such as the bones, muscles, nerves, 

 lungs, blood, which show tension and pressure in their functions. 



The bones, by supporting each other, act on each other 

 mechanically ; for the motion of the body is a succession of 

 falls, which permit alternations of pressure and rest upon the 

 limb-bones. Thus, if we take the humerus, for instance, it 

 Avill be found most extended in the direction between the 

 radius and the scapula, in which it has, when in mechanical 

 use, to support and lift the weight of the carcass. If the ends 

 are examined, where rotation or movement is permitted, it will 

 be seen that pressure is experienced over a wider area than is 

 possible in the section of the shaft, which only serves as a 

 prop. Hence, and partly from the attachment and pressure of 

 other organs, the articular ends of bones are enlarged ; but it 

 is probable that something of the enlarged size of the ends of 



