504 OF NUTRITION. 



644. From the foregoing details the obvious inference results, that each 

 part of the organism has an individual Life of its own, whilst contributing to 

 uphold the general Life of the entire being. This Life, or state of Vital Action, 

 depends upon the due performance of the functions of all the subordinate 

 parts, which are closely connected together. The lowest classes of organized 

 beings are made up of repetitions of the same elements ; and each part, there- 

 fore, can perform its functions in great degree independently of the rest. But, 

 in ascending the scale, we find that the lives of the individual parts become 

 gradually merged (so to speak) in the general life of the structure ; for these 

 parts gradually become more and more different in function, and therefore 

 more and more dependent on each other for their means of support ; so that 

 the activity of all is necessary for the maintenance of any one. Hence the 

 interruption of the function of any important organ is followed by the Death 

 of the whole structure ; because it interferes with the elaboration, circulation, 

 or purification of that nutritious fluid which supplies the pabulum for the 

 growth and reproduction of the individual parts. But their lives may be pro- 

 longed for a greater or less duration, after the suspension of the regular series 

 of their combined actions ; hence it is, that molecular Death is not always an 

 immediate sequence of somatic Death.* But if the function of the part 

 have no immediate relation to the indispensable actions just adverted to, it may 

 cease without affecting them ; so that Molecular death may take place, to a con- 

 siderable extent, without Somatic death necessarily resulting. 



645. The doctrine of Development from Cells has another important bearing 

 on the Philosophy of Physiology. It gives us a clearer idea of the nature of 

 the continual processes of decay and renewal, which take place in the Animal 

 body. Every Cell has, to a certain degree, an individual life of its own. 

 This individuality is much more decided in the lower forms of organized being, 

 where each cell can maintain an independent existence, than it is in the higher, 

 in whose fabric a large number having different functions are united into one 

 structure, the combined activity of the whole of which is necessary to the life 

 of any one. But, even in the highest, it is evident that each cell will possess 

 a certain duration of its own ; and that, from its first period of development, 

 all the changes which it undergoes are governed by laws peculiar to it. In the 

 various parts of the Vegetable, as in those of the Animal, we find a great dif- 

 ference in the duration of the existence of the cells composing them. These 

 differences may be reduced to five heads. 



I. Cells may be generated, which have a very transient existence, and which 

 disappear again, without reproducing themselves, or undergoing any trans- 

 formation. This may be seen in the Vegetable ovule, and in the Germinal 

 Vesical of the Animal Ovum ; as well as in many other parts. Thus we have 

 absorbent Cells ( 461), secreting Cells ( 651), and probably Assimilating 

 or Fibrin-elaborating Cells ( 578) ; all of which originate in pre-existing 

 germs, attain their full development (in the course of which they perform their 

 allotted function), and then disappear by rupture or liquefaction. In such in- 

 stances it is obvious that, from their first origin, the cells are subject to a law 

 of limited duration, and that their death and decay are as much the result of 

 their inherent constitution, as are those of each entire Animal or Vegetable or- 

 ganism. 



II. The contrary extreme to this may be found in those Cells of which the 

 function, instead of being transient, is to be indefinitely prolonged ; such are 

 those of which the organs of mechanical support are usually formed. Here 

 the cell, instead of changing its form, or of giving origin to new cells within 

 itself, becomes the subject of an internal deposit of hard matter, which lines 



* Cyclop, of Anat. and Phys., vol. i. Art. Death. 



