ORGANIC DEPENDENCE AND DISEASE 15 



PROTECTIVE COVERING A BASIC FACTOR 

 IN DEPENDENCE 



A knight in armor is a protected fighter and by his pro- 

 tection increases his viability. A man *'on his own," who 

 fights with his ^' dukes," risks his viability but nevertheless 

 increases his physical vigor and exalts his bodily prowess. 

 A recent writer on the morale of our army in France brings 

 out the fact that a man who could defend himself with his 

 fists made a better soldier than the one who depended alone 

 on the weapon he carried in his hand. 



Nature has given to a large part of the animal world one 

 or the other of two solid supports for the soft organs and 

 flesh of the body ; an inside skeleton, like that on which our 

 own soft anatomy is hung, or an outside skeleton or shell, 

 to which we may here give special attention. I have used 

 the expression, nature has given, meaning that the neces- 

 sity of support to the body having early shown itself, such 

 supports developed in response to external impacts and 

 internal stresses ; the historical course of development of 

 these calcareous supports makes the fact sufficiently obvi- 

 ous that they are a determined sequence and not a chemical 

 reaction or a casual device. 



A rhizopod, a speck of soft protoplasm with the mar- 

 vellous special function of eliminating the silica from its 

 solution in the sea, exudes this mineral matter in the 

 form of an outside shell of wondrous delicacy and sym- 

 metry. The unprotected soft tissue in the primitive ances- 

 try of all the great tribe of the Mollusca or shell-fish, tossed 

 haphazard on the sea bottom and hopeless against attack 

 except through concealment or powers of rapid self -propul- 

 sion, acquires the special function of eliminating from the 

 sea the salts of lime, carbonate or phosphate, and with them 

 builds up its outside shell. We have just noticed that even 

 today the young of such hard-shelled moUusks, in stages 

 when their shells are but beginning to grow, are free swim- 



