THE BIOLOGY OF DAILY LIFE. 



CHAPTEE IV. 



HOW THE LAW OF INTERCHANGE EXPLAINS THE RELATIONS 

 BETWEEN THE BODY AND LOWER ORGANISMS, PARTICU- 

 LARLY MICRO-ORGANISMS, IN HEALTH AND NATURAL 

 DECAY. 



WE have already seen enough to account for a large 

 part of the diseases which afflict humanity, in the vio- 

 lation of one of the fundamental laws of well-being ; 

 a violation which has been practised long ago, and 

 handed on from generation to generation, and, amidst 

 all changes, unhappily maintained. 



There is another law, or rather a further statement 

 of this fundamental law of Biology, upon which we 

 have not yet touched, and which we shall find is, if 

 possible, more closely connected with our physical 

 well-being than any we have yet considered. This 

 may be stated thus : 



THE EXISTENCE OF ANY ORGANISM DEPENDS UPON 

 ITS BEING ABLE TO MAINTAIN A PROCESS OF CHANGE, 

 IN CONTINUOUS ADJUSTMENT WITH ITS SURROUNDINGS, 

 AND TO DO SO IT MUST MAINTAIN A STRUGGLE AGAINST 

 OTHER ORGANISMS. 



These opponents in the battle of Life may be either 

 of the same or of different kingdoms ; vegetable versus 

 vegetable, animal versus animal, or vegetable versus 

 animal. 



The rule appears to be invariable that a higher, 

 that is, a more differentiated organism, is liable to be 

 attacked by hosts of organisms lower in the scale of 

 differentiation. 



