i66 THE POPULAR SCIENCE MONTHLY. 



the fragments to move one against the other, become covered with 

 cartilage and encapsulated with fibrous and ligamentous tissues, so as 

 to form the " false joint " of surgeons. Mucous membranes, when con- 

 tinuously exposed to the air, adapt themselves to their new situation 

 by becoming covered with a layer of epidermis closely resembling 

 skin. Of this we have a good illustration in long-standing cases of 

 procidentia uteri^ where the vaginal mucous membrane is often con- 

 tinuously exposed. 



The vegetable world also furnishes numerous illustrations showing 

 how plants adapt themselves, by modification of structure, to new 

 conditions in which they have been placed. The geranium in our win- 

 dow, instead of growing in its naturally vertical direction, disposes its 

 twigs and branches obliquely on one side, thereby adapting them, 

 their leaves, blossoms, etc., the better to receive the rays of light that 

 come in slanting through the window. Plants kept more or less in the 

 dark, have a deficiency of color ; they become bleached and white, but 

 this lessened opacity of their skin, this increased transparency of tis- 

 sue, enables them to make the most of what little sunshine is allotted 

 them. 



The sprouts of an onion or potato, when kept in a dark chamber, 

 grow to an unusual length, and, although this elongation can accom- 

 plish no good when the bulb is packed in a barrel, or housed in a cellar, 

 still it is evident that the plant is obeying the same laws of adaptive 

 growth by which, when buried deeply in the earth, its sprouts increase 

 in length until they reach the sunny surface of the soil. 



Now, while these instances (and many others might be added) cer- 

 tainly furnish unequivocal evidence of a disposition on the part of 

 organs and organisms to adapt themselves to new conditions in which 

 they have been placed, and to altered functions they have been re- 

 quired to execute, yet it must be admitted they exhibit little or no 

 proof that those other organic alterations, which we regard as fatal 

 diseases, are imbued with the same conservative design. In fact, to 

 meet the issue at once to strangle the serpent before we take out his 

 fangs it is necessary to dispose of the objection that organic diseases, 

 structural formations resulting from pathological development, pro- 

 duce physical pain, and lead to death ; for that they do so is the com- 

 mon belief. 



To meet this objection it is simply required to follow out the anal- 

 ogy, already alleged, between structures resulting from j^hysiological 

 development and those produced by development that is pathological. 

 That the causes and objects of the two kinds of growths are the same, 

 has been previously intimated. We proceed by calling attention to 

 (what may surprise those who have not given the subject proper con- 

 sideration) the great fatality attending physiological evolution: 



Very young animals, and indeed young plants, are peculiarly liable 

 to die before reaching maturity. This is especially the case in animals, 



