TO PHYSICS AND PATHOLOGY. 17 



However true it may be that augmentation in the mass of an organic body be 

 occasioned by the force of attraction, there is no resemblance externally between 

 the growth of a crystal and the formation of an organism. The form of the 

 membrane is not affected by the physical form of the atom, as it is in crystals, for 

 instance, in a crystal of alum, consisting of an aggregate of particles of alum, where 

 each individual crystal has a form precisely similar to that of the aggregate body 

 The cell is a whole within itself, and not an aggregate of smaller cells. 



EXPLANATION. 



Crystals have not, like cells, a limit of growth : the increase of size in the 

 crystal is not occasioned by a cause acting from within in an outward direction, as 

 in living organisms, but by the force of attraction upon the surface. This force is 

 active at every point of the outer surface, while the molecules below take no part 

 in the growth, and may even be removed without depriving the superficies of their 

 capacity to increase. The new planes which are formed on truncating the angles 

 of a crystal, exercise no stronger attraction on the molecules of the surrounding 

 medium, than do the other planes ; and they do not in any special manner perfect 

 themselves. 



By cutting off an angle from an octahedron we obtain a cubic superficies of the 

 crystal, bounded by four converging octohedric planes ; in a crystalizing fluid the 

 body increases in three dimensions ; the four superficies become longer and 

 broader, and, in consequence of their elongation and convergency, the angle is 

 restored, even when the cubic superficies has been incrusted. But when one angle 

 is struck off a cubic crystal of alum, and the crystal be thus truncated, it does not 

 increase, in the mother liquid, in a greater degree towards the truncated angle than 

 towards any of the other sides ; the original cube-like figure is not restored, 

 because the force of attraction of one individual portion of a cubic plane is not 

 greater than the attractive force of an equally large portion of any one of the six 

 superficies of the outer surface. 



A crystal which grows in a saturated solution, always increases on one side 

 especially, that is, on the surface directed towards the bottom of the vessel, owing 

 to this plane being always in contact with those particles of the saline solution, 

 which have the greatest specific weight, and are most copiously charged with the 

 crystallizing matter. There are also cases in which, in consequence of the differ- 

 ence of temperature of the upper surface and the bottom of the vessel, the 

 crystal increases most in a downward direction, while the upper parts lose their 

 form. 



COMPARISON OF THE PARASITE THEORY WITH THE CHEMICAL 

 THEORY OF CONTAGION, MIASMA, AND PUTREFACTION. 



The source of the most frequent errors in judging of a condition of disease, 

 originates in regarding things that frequently occur simultaneously, as necessarily 

 exercising a mutual influence on each other ; looking upon the one as the cause of 

 the other. For the comprehension of diseased conditions and the choice of means 

 to remove them, there is no view which is more deficient in a scientific basis, than 

 that of identifying miasma and contagion with living organisms, as parasites, fungi, 

 and infusoria ; and regarding them as being developed and increased in the healthy 

 body, where they thus induce a condition which may terminate in death. 



A glance at the principles of the parasite and chemical theories, will suffice to 

 show the respective merits of each. 



But if, in the following remarks, I attempt to lay before my readers, by means 

 of a series of facts, certain processes of the living organism, together with their 



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