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Untitled Article
^ phe uses or purpose of the circulation we must give in the lecturer ' s o « % words . * To afford to the capillary arteries a due supply of arterial blood is the ultimate object of all the apparatus of the circulation , and of all its fcctkm . By the capillary arteries it is that nutrition is effected , that secretion is performed , that structure is built up . When the blood
has been delivered into these vessels what happens to it ? What changes are wrought upon it , and by what agencies ? We have seen that the great bulk of the arteries terminate in the tissues , in mem"braneless canals ; that where the arteries thus terminate the blood flows in canals formed in the substance of the tissues , not in proper vessels . We have seen that in proportion as the membranous tunics
of the arteries diminish in thickness and strength , the nervous filaments increase in number and magnitude . We have seen that when the processes which now go on are carefully observed with the microscope , particle 3 of blood can be seen to pass from the current of the circulation , and to mix and mingle with the particles that constitute the substance of the organs ; while particles that form the substance of the organs repass in their turn into the circulation . 4
Thus far the successive steps of these curious processes are objects of sense ; but here we are only on the very confines of the domain of life , and beyond this we have hitherto not been able to penetrate . What the peculiar agents are which are now called into action , and to wliat laws they are obedient we do not know . The agents are distinguished by the name vital ; the actions we refer to certain general principles , of which we know nothing , but which we term Vital affinities . 4
We see that changes are now wrought upon the blood ; we see that its chemical composition is subverted ; we see that its constituents enter into new combinations ; we see that these changes go on in a certain order and according to fixed laws , and these we designate Vital affinities . Arterial blood is conveyed by the larger arteries to the capillaries ; but the capillaries no where give out , no where deposit arterial blood . Arterial blood is conveyed by the branches of
the carotid arteries to the capillaries of the brain ; but the capillaries of the brain do not deposit blood in the brain , they deposit brain . Arterial blood is conveyed by the nutrient arteries of bone to the capillaries of bone , but the capillaries of bone do not deposit b \ oody they lay down osseous particles . Arterial blood is conveyed by muscular branches to the capillaries of muscle , but the capillaries of muscle do not deposit blood in the muscle , they lay down muscular fibre . The
blood conveyed to the capillaries of brain , to the capillaries of bone , to the capillaries of muscle is precisely the same ; all comes alike from the left heart ; all is conveyed alike to the different organs by similar tubes . Yet the capillaries of the brain convert their blood into brain ; the capillaries of bone into bone ; the capillaries of muscle
into muscle . For this reason these capillaries have been termed the chemists of the system , and subtle and elaborate chemists they are ; and the various organs have been regarded as so many different laboratories , specifically adapted to the purpose , where the various processes that are carried on in the economy are conducted . Out of one and the same fluid , the blood , these vessels manufacture cuticle ,
Untitled Article
200 Dr . Sontkwood Smith on the Animal Economy ^
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Citation
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Monthly Repository (1806-1838) and Unitarian Chronicle (1832-1833), March 2, 1833, page 200, in the Nineteenth-Century Serials Edition (2008; 2018) ncse.ac.uk/periodicals/mruc/issues/vm2-ncseproduct2610/page/56/
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