1815.) Vascular and Extra Vascular Paris of Animals. 175 
ferences to be drawn from them, are connected with the previous 
establishment of definite views, of clear intelligible terms, and of 
strict physical methods; and feeling the importance of the present 
subject, I hasten to submit this memoir to competent judges. 
1 am aware that premature generalizations of facts, as well as 
premature inductions from them, are seldom useful ; and I should 
not have troubled the scientific inquirer with this communication, 
had I not felt assured that the present state both of anatomy ‘and 
physiology would authorise it. In my statements I shall purposely 
avoid all metaphysical pretension to dive into the hidden mystery of 
vitality, confessing myself wholly incompetent to reduce that power 
within the rules of physical science : a power which appears to my 
judgment as allied to the nature of an inscrutable First Cause, or 
as an emanation from it. 
The vast variety in the substances, texture, bulk, and combina- 
tions, which the living animal and vegetable kingdoms exhibit, 
renders it difficult to define the essential residence of life as con+ 
nected with any of the modes of organic structure. Some of the 
compounds and textures of animals are known to be more important 
for the maintenance of life than others, as the cerebral substance 
and the muscular textures; but there is a numerous tribe of living 
bodies that appear to be wholly destitute of those peculiar parts, of 
which the entire vegetable kingdom may be adduced as an instance. 
Habits of meditation and research have led me to conclude that ‘ 
some benefit may arise to physiology from more accurate discrimi- 
nations between the several substances of living bodies; especially 
as to the relative dominion of vitality, or of physical causes on those 
substances respectively. 
The active phenomena of life appear to be generally distinct 
from those of physical causation ; but the passive condition of living 
substances is not so obvious. The suspended actions of torpid ani-— 
mals and vegetables, and the latent vitality of many of the more 
simply constructed animals and vegetables during the absence of 
heat and moisture, show the intimate connections which subsist 
between vitality and physical causes. Difficult and intricate as the 
investigation may seem when extended to all the cases of vital phe- 
nomena, they are not so in the grosser examples to be now adduced; 
and if it should be found that many substances distinctly continuous 
: with vital organic bodies are wholly subjected to physical dominion, 
and that several other substances are in part influenced by the one 
eause and by the other, it may perhaps open new and more precise 
_ views in the medical art. Those parts of living organic bodies which 
_ have no power of self repair, which hold no continuity with the 
fluid circulating material destined to replenish the waste, to augment 
the bulk, or repair the accidents of the living fabric, may be justly 
| deemed extra vital. The exuvial coverings and defences of animals 
are of this kind, viz. hairs, nails, feathers, and all other cuticulat 
| structures, as well as the epidermoid coverings or husks of the 
vegetable kingdom. Some of those substances which are destined 
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