Bauhaus-Universität Weimar

284 
ORGANIC ASSIMILATION. 
Fibrin or muscle is said like yeast, to excite fermentation in solu¬ 
tion of sugar. Dr. J. Davy, however, on performing the experi¬ 
ment with beef, and continuing it three or four days, obtained gum 
in place of alcohol. {Kastner's Archiv. 1831, p. 396.) The organic 
digestive principle, or “ pepsin/7 secreted by the walls of the stomach, 
dissolves coagulated albumen and fibrin vejy readily, even out of 
the body, and so modifies their composition that they acquire different 
chemical properties. In the animal system, however, the action 
of organic fluids on one another is modified by the vital principle. 
The action of saliva and of bile in the process of digestion, is not 
intelligible from the effects which they produce on organic com¬ 
pounds out of the body. The processes just alluded to, and, perhaps, 
those mentioned in the following paragraph, also, appear to belong to 
that class of chemical actions to which Berzelius (Fortschritte d. phy¬ 
sisch. Wissensch. Bd. 15. pp. 237-247,) has given the name “cata¬ 
lytic.77 They are actions in which a certain matter by its presence 
gives rise to decompositions or combinations in other substances, 
without itself undergoing any appreciable change. Thus, the pre¬ 
sence of sulphuric acid decomposes alcohol into ether and water; 
finely divided platina and other metals cause hydrogen and oxygen 
to unite suddenly. Dilute sulphuric acid acting upon starch, con¬ 
verts it into sugar, and an organic substance called “diastase,77 found 
in abundance in the buds of the potato, effects the same change in 
the starch of that tuber; a change necessary for the nutrition of the 
plant. Thousands of such catalytic actions, Berzelius remarks, are, 
probably, going on in the economy of organised bodies. It has been 
recently stated by M. Fremy, (Comptes Rendus, 1839, Juin 17 and 
Juillet 30,) that many animal membranes, but particularly that of 
the calf7s stomach, have the property of converting sugar of milk 
and other saccharine substances into lactic acid, and organic salts, 
such as the citrates, malates, and tartrates of potash and soda, into 
carbonates, when solutions of these substances are brought into con¬ 
tact with them out of the body; and that the membranes themselves 
seem to undergo no change since the same portions of them serve 
for repeated experiments. All these facts strengthen the probability 
of the view, that the changes of composition constantly going on in 
organic bodies, do not essentially differ from the ordinary chemical 
changes. The production of the different secretions even may de¬ 
pend on peculiar “catalytic77 actions of the walls of the secreting 
canals. 
5. Organic assimilation is evinced in the changes of composition 
which organic fluids undergo, while exposed to the influence of living 
surfaces endued with the vital principle. Thus, the composition of 
the chyle absorbed from the alimentary canal undergoes a change in 
the lacteal system; the quantity of fibrin that it contains being greater 
in proportion to the number of mesenteric glands through which it 
has passed. In the formation of the different secretions the same 
action of the tissues on the fluids takes place, but in a modified form, 
inasmuch as the components of the blood, which have been changed 
by the action of the tissues, are in this case separated from it.
        

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