10 Development and Maintenance. 



Maintenance has been going on throughout the 

 whole of this time. Functional activity is at- 

 tended by a process of waste or decay of the 

 parts implicated. This process will be hereafter 

 expressed as metamorphosis of tissues. 



In no period of life can this process be said 

 to be dormant or non-existent, but in none so 

 slow or so little required as in early youth. At 

 this time the building up of the animal body by 

 the accumulation of blood, bone, muscle, hoof, 

 horn, teeth, hair, &c., &c., is actively carried on, 

 and their waste or decay comparatively small. 

 In adult life, however, when development has 

 gone on to completion, and great exertion is 

 called forth, metamorphosis or change in the 

 constitution of the tissues above mentioned is 

 great. 



This requires the process of maintenance or 

 repair to restore, during repose, that which has 

 being constantly lost during activity or exercise. 



The movements of the arms or legs in walk- 

 ing, the tongue and jaws in speaking, lungs 

 during respiration, heart in its beating, and in- 

 testines during contraction, in short, any act, 

 voluntary or involuntary, which calls forth mus- 

 cular movements in any part of the animal body, 

 is attended with the expenditure of vital force, as 

 shown in the change or alteration of the condi- 

 tion, waste, decay, or metamorphosis of the com- 

 posing material. 



During metamorphosis of tissue chemical 



