Inquiry into the Nature and Properties of the Blood. 25 1 



of the Vital Principle, the Anima of Stahl, the Animal Spirits 

 of Des- Cartes, the Nervous Fluid, the Galvanic Fluid of some 

 late writers, the Vis Medicafiix Natiirce of CuWen, the Materies 

 Vitce diffusa of Hunter, the Principle of Irritability. All these 

 notions, however, have failed to satisfy the mind, which is averse 

 from conjecture, and which exults at beholding truth in its 

 own light ! When we observe, therefore, that certain specific 

 purposes and designs are fulfilled and accomplished by the 

 organic structures that are displayed before us in all the ani- 

 mal and vegetable creation in such an endless variety, — when 

 we observe that these structures depend momentarily upon the 

 presence of a fluid answering to blood, by virtue of which 

 alone they live, and thence by living, act, — when we observe 

 that there are gradations of excellence in the condition of the 

 blood, and that the higher or the more exalted the condition, 

 the more wonderful is the organization which is produced 

 from and preserved by it ; — we admire the gradation of ex- 

 istence, the subordinate dependence of one thing upon an- 

 other: we behold the perpetual relationship and distinction 

 between cause and effect maintained and adhered to ; the order 

 of subsistence to be that of existence: in short, we discern the 

 rules of true philosophy scrupulously observed, and her axioms 

 supported and substantiated by all our experience. 



With these principles in mind, we have followed the suc- 

 cessive gradations of development as represented in the for- 

 mation of the chick in the egg, and as described by several 

 patient observers of this process from first to last. A gelatinous 

 molecule, as it is called by Sir E. Home, from which the fu- 

 ture embryo is to be formed, would appear to the naked eye 

 as a most confused, indeterminate fluid ; but is found by the 

 microscope to have its centre made up of globules ttuVo*^^^ P^^^ 

 of an inch in diameter, surrounded by circles of a mixed sub- 

 stance, made uj) also of small globules and of some that are 

 larger and oval-shaped. 



From this, as from a commencing point, the work of for- 

 mation proceeds ; the albumen or white and yolk of the egg 

 are nothing else than materials suited exactly to the purposes 

 and objects intended by this molecule or forn)ative substance, 

 and derived, like the elements of the molecule itself, from Na- 

 ture's stores. The white and the yolk of the egg respectively to 

 the molecule, are jmssive in the first stage of formation ; but 

 as these stages proceed, the elements of which they consisted 

 are elevated into a new condition, and in this conilition form 

 a part of the thence increasing and developing animal ; they 

 tlius l)ecoiMe relatively to the remaining ))ortion oi' the white 

 and yolk of the egg, active and living; and thence, by virtue of 



2 K 2 their 



