1819.] and on the Blood in general. | 275 
albumen, but that this change nevertheless takes place after- 
wards either in consequence of the original tendency given to it 
in the duodenum, or of the subsequent action of the absorbent 
vessels, &c. through which it passes. If it be objected -as 
unlikely that the lacteals should take up such imperfectly 
formed and crude materials, it may be answered that they often 
take up substances much more dissimilar to those which are 
natural to them, as has been often found by actual experiments 
made with musk, colouring substances, &c. and indeed, .as is 
sufficiently proved by daily experience, with medicinal substances, 
many of which do not appear to operate till taken into the mass 
of blood. 
My readers will doubtless remark, that I have not mentioned 
the existence of fibrinand the red particles in the duodenum, 
which ought to be the case, provided the original notion, stated 
at the commencement of this essay, were well founded. To this 
I answer, that although I never could completely satisfy myself 
of the actual existence of fibrin in the duodenum, yet | often 
noticed that its contents underwent a distinct and remarkable 
change on exposure to the air, and which appeared analogous 
to that sort of dissolution which we stated the coagulum of 
chyle to undergo when placed in similar circumstances ; that is 
to say, from being generally of a glairy and rather firm consist- 
ence, they became, after an hour or two, thin and ichorous. 
That fibrin, however, is occasionally, if not always, formed in 
the duodenum, is very probable, from its being found in the lac- 
teals immediately after it has been taken up from the intestines. 
Some indeed may feel inclined to attribute its formation to the 
act of absorption; but from what has been said above, it seems 
very likely that this is little else than a mechanical process. 
With respect to the red particles, they certainly do not exist as 
red particles in the duodenum, nor even, perhaps, in the chyle 
itself; whzte particles, however, are found in the chyle at avery 
early period of its formation, and these, in part at least, appear 
to have the property of becoming red on exposure to the air; 
for chyle, as we formerly stated, assumes a pinkish hue after it 
has been removed some time from the thoracic duct. These 
white particles, therefore, are probably the same as the red 
particles, the red colour not being developed (at least completely) 
till they have been exposed to the action of the air in the lungs. 
There is, however, evidently another variety of white particles in 
the chyle besides those destined to become the future red parti- 
cles. These are much larger, and appear to be formed of the 
caseous-like and oily principles stated to exist in chyle, and 
which are insoluble in the serous portion, and, therefore, natu- 
rally assume the globular form, like oil diffused through water. 
Lastly, We have to consider the mode of action, &c. of those 
agents which‘operate in the production of the mysterious pheno- 
mena of assimilation ; and upon this part of the subject it must 
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