136 
REVIEW. — A TREATISE ON 
from the circulation, and becomes organized and endowed with 
vitality. Such is the capillary circulation, as widely diffused 
throughout the kingdom of nature as life itself. It is found in full 
force, after heart, arteries, and veins, have disappeared; and it is 
acting in foetal life long before the development of any of these 
vessels. 
“ II. Nutrition. This process consists in the several solids al- 
ternately receiving from and returning to the nutritive fluid a suc- 
cession of particles similar to those of which their structure is 
already composed. The blood which circulates through the system 
of capillary vessels, has, when viewed with a microscope, been 
compared to a sort of whirlpool, from which various particles are 
constantly thrown off to the different solids, while others are de- 
tached from the solids, and flung back into the vortex of the circu- 
lation. 
“ III. Secretion. In the intimate structure of every tissue, or 
whenever a particle of the nutritive fluid comes in contact with a 
particle of living matter, there is a fluid produced, often without 
the aid of any peculiar secretory apparatus, and otherwise by a 
distinct glandular one. 
“ These three phenomena comprehend the fundamental princi- 
ples of organization in all beings; but in man and in animals a 
fourth action is superadded, which exercises a powerful influence 
and control over the nervous system, is the seat and instrument of 
this action, and its influence over the acts of circulation, nutrition, 
and secretion, is the more absolute and indispensable, the more ele- 
vated the rank the animal occupies in the scale of existence. 
“ Finally, since all the materials of nutrition and secretion are 
derived directly from the blood, and since the blood contained in 
the capillary vessels differs in no respect from the general circu- 
lating mass, it follows that the qualities of the general mass of 
blood must exercise a very material influence over all the pheno- 
mena of nutrition and secretion. Hence it is that, in beings that 
have centres of nervous influence and a systemic circulation, the 
life of each part is involved in the life of the whole, and there 
arises that relation of so many different actions to the whole and to 
each other which constitutes the unity of the living system. The 
animal in a state of disease exhibits certain modifications of those 
actions that are essential to health. The supply of blood may be 
different in quality, and hence will arise lesions of the circulation. 
The component particles of the different solids may be altered in their 
arrangement, order, number, consistence, or nature ; hence lesions of 
nutrition. The different fluids separated from the blood may be 
altered in quantity or quality ; hence lesions of secretion. The 
state of the nervous system, and the composition of the blood, 
