270 Dr. Prout on the Phenomena of Sanguification, [APRIL, 
ing, and when the chyle may be supposed to be entering the 
sanguiferous system, but I have not myself observed this circum- 
stance. With respect to these observations in general, | am 
fully aware that they are too limited and imperfect to be much 
relied upon, though I am persuaded that if this part of the subjeet 
were duly investigated, it would throw a greal deal of light on 
this obscure function. Imperfect as they are, however, they are 
sufficient to account in some degree for the very great differences 
in the quantity of carbonic acid gas, said to be given off by 
different individuals, as stated in the preceding section. As far 
as I am aware, no similar experiments have been made on the 
inferior animals. 
Fifthly, We come to consider whether the blood as a whole, 
or in part only be concerned in the production of these pheno- 
mena. This question cannot be easily decided by experiment. 
it appears, however, from some observations of Berzelius, that. 
the colourmg matter of the blood is the principle from which the 
carbon is chiefly derived in respiration. “ It has been generally 
believed,” says this accurate observer, “that every part of the 
blood is influenced by the air; that it absorbs oxygen, and 
exhales carbonic acid gas ; but this is not the case. Blood, in 
which the colouring matter is still contained, absorbs oxygen 
gas very quickly when out of the body, and shaken in atmo- 
spheric air; it also retains at the same time some part of the 
carbonic acid thereby produced; on the other hand, serum, ~ 
when destitute of colourmg matter, does not change the atmo- 
spheric air before it begins to putrefy.” * The colouring matter, 
however, appears to possess this property in its natural state 
only ; and whilst it is in contact with the other principles of the 
blood; for if it be separated and diluted with water, it seems no 
longer capable of beg affected by the contact of atmospheric 
air; at least, it undergoes no change in colour.+ This is a very 
important fact, and deserves to be better investigated. 
We come now to consider a little more closely the phenomena 
and nature of these mysterious processes, by which substances 
foreign to animal bodies are assimilated to their nature. 
The nature of the digestive process has engaged the attention 
of physiologists from the earliest times ; and the aid of all the 
various physical agencies and sciences which happened to 
occupy the attention of philosophers at the time, has been suc- 
cessively called in to explain its phenomena. By Hippocrates 
it was attributed to a sort of concoctive fermentation. By Galen 
and his followers, chiefly to heat. By Helmont, to his archzeus. 
By the Jatro-mathematici, to trituration. By Pringle and Mac- 
bride, to fermentation. And, lastly, by Hunter, Spallanzani, and 
most physiologists since their time, to the agency of a peculiar 
* See Berzelius’s View of the Progress and Present State of Animal Chemistry, 
p. 36. 
+ See Observations and Experiments on the Colour of the Blood. By W. C. 
Wells, M.D. F/R.S. Phil. Trans, 1797, Part II. 
