26 NUTKITION. 



of every living body, we discover a union of solids 

 and fluids ; the solid parts consisting of minute 

 particles, so arranged as to form fibres and tissues 

 of various density and structure. Everywhere these 

 solids are pervaded by a circulating fluid, from which 

 the particles composing them are elaborated, and by 

 means of which the organic system is nourished. 

 When we attempt to investigate the intimate texture 

 of the solids beyond a certain point, we are foiled ; 

 no eye can scan, no instrument can follow, the 

 mysteries of organic structure, or its circulating 

 fluids. 



As vitality is essential to the circulation of the 

 fluids of the system, so it is by the same power that 

 certain tubes are enabled to absorb particles of 

 extraneous matter, carry them into the mass of cir- 

 culating fluid, and become incorporated with the 

 body. On the other hand, the system throws off 

 by transpiration, particles which, having been in- 

 tegral portions of itself, are now useless ; and hence 

 it may with truth be said, that no living body is, 

 after a certain period, the same, particle for particle, 

 as it was, though its identity remains. From this 

 view we shall be readily led to conclude, that a due 

 proportion of aliment is required, in order that the 

 loss be counterbalanced ; and that where this is 

 withheld, the- -body becomes emaciated, till at last 

 the vital energies yield, and no longer sustain the 

 organic structure. But in order to the growth of 

 an organic body, the accession of particles must 



