90 SYMBIOGENESIS 



To the question why in individual descendants of animals 

 the limit of modification is but slowly extended, Herbert 

 Spencer replies "that there are required numerous and wide- 

 spread modifications." In other words, there is a plurality of 

 correspondences and correlations to be considered. With his 

 usual brilliancy and wealth of illustration, Spencer shows how 

 these correspondences work out in the purely physiological 

 sphere. He takes no account, however, of the most essential 

 of all, viz., the bio-economic sphere and its correspondences, 

 which latter primarily determine the constancy or otherwise of 

 all equilibria concerned. 



Before the artery which feeds a hard-worked muscle can permanently 

 furnish a large additional quantity of blood it must increase in diameter 

 and contractile power, and that its increase of diameter and contractile 

 power may be of use the main artery from which it diverges must also 

 be so far modified as to bring this additional quantity of blood to the 

 branch artery. Similarly with the veins, similarly with the absorbents, 

 similarly with the nerves. And when we ask what these subsidiary 

 changes imply, we are forced to conclude that there must be an analogous 

 group of more numerous changes, ramifying throughout the system. The 

 growth of the arteries primarily and secondarily implicated cannot go 

 to any extent without growth in the minor blood-vessels on which their 

 nutrition depends, while their greater contractile power involves enlarge- 

 ment of the nerves which excite them and some modification of that 

 part of the spinal cord whence these nerves proceed. Thus, without 

 tracing the like remote alterations implied by extra growth of the veins, 

 absorbents and other agencies, it is manifest that a large amount of 

 rebuilding must be done throughout the organism before any organ of 

 importance can be permanently increased in size and power to a great 

 extent. Hence, though such extra growth in any part as does not 

 necessitate considerable changes throughout the rest of the organism may 

 rapidly take place, a further growth in this part, requiring a remodel- 

 ling of numerous parts remotely and slightly affected, must take place 

 but slowly. 



Although Spencer does not perceive that nutrition which 

 here comes in without proper introduction is primarily deter- 

 mined by work, yet this passage marks a noticeable approach 

 to our bio-economic theory, so long as we tacitly imply that the 

 organism having need of food and of occasional rebuilding 



