144 



ON THE CIRCULATION OF THE BLOOD, 



materials first, a peculiar aroma, or odour, of which every one must be 

 sensible who has been present at a slaughter-house on cutting up the fresh 

 bodies of oxen ; secondly, fibrine, or fibrous matter ; thirdly, uncoagulable 

 matter, but no gelatin, which is a subsequent secretion; fourthly, albumen; 

 fifthly, red-colouring matter; sixthly, iron; seventhly, sulphur; eighthly, 

 soda ; and, lastly, water. The proportion of these parts vary almost infinitely, 

 according to the age, temperament, and manner of living; each of these 

 having a character that essentially belongs to it, with particular shades that 

 are often difficult to be laid hold of. 



Of these component parts, the most extraordinary are the red-colouring 

 matter, the iron, and the sulphur ; nor are we by any means acquainted with 

 the mode by which they obtain an existence iri the blood. I have already 

 had occasion to observe, that albumen and fibrine are substances formed by 

 the action of the living principle out of the common materials of the food, and 

 that it is probable the lime found in the bones and other parts is produced in 

 the same manner. Whether the iron and sulphur that are traced in the blood 

 have a similar origin, or exist in the different articles of our diet, and are 

 merely separated from the other materials with which they are combined, is 

 a physical problem that yet remains to be solved. It should be observed, 

 however, that the sulphur does not exist in a free state even in the blood itself, 

 but is only a component part of its albumen. Considering the universality of 

 these substances in the blood, and the uniformity of their proportion in similar 

 ages, temperaments, and habits, whatever be the soil on which we reside ; 

 that those who live in a country in which these minerals are scarcely to be 

 traced have not less, while those who live in a country that overflows with 

 them have not more ; it is perhaps most rational to conclude, that they are 

 generated in the laboratory of the animal system itself, by the all-controlling 

 influence of the living principle. 



The exact proportion of sulphur contained in the system has been less ac- 

 curately ascertained than that of the iron, which last in an adult, the weight 

 of whose blood may be estimated at 281bs.,* ought usually to amount to 

 seventy scruples, or about three ounces : and hence the blood of about forty 

 men contains iron enough to make a good ploughshare, and might easily have 

 its iron extracted from it, be reduced to a metallic state, and manufactured 

 into such an instrument. 



Iron is seldom found except in the red particles of the blood ;t and it has 

 hence been supposed by the French chemists to be the colouring material 

 itself. The process of respiration, according to the theory of Lavoisier and 

 Fourcroy, is a direct process of combustion, in which the animal system 

 finds the carbon, and the atmosphere the oxygen and caloric ; and in conse- 

 quence of the sensible heat which is set at liberty during the combustion, 

 the iron of the blood is converted into a red oxide, and hence necessarily 

 becomes a pigment. 



But it is impossible to ascribe the red colour to this principle : for, first, we 

 are by no means certain that the air communicates any such substance as 

 caloric to the blood ; and, secondly, let the sensible heat of the blood arise 

 from whatever quarter it may, it can never be sufficiently augmented by the 

 most violent degree, either of local or general inflammation, to convert the iron 

 of the blood into a red oxide, which, indeed, is never produced without rapid 

 combustion, flame, and intense heat. And hence. Sir Humphry Davy con- 

 jectures the carbon itself of the blood to be the real colouring material, and to 

 be separated from the oxygen, with which it is necessarily united to constitute 



* Blumenbacb states the proportion in an adult and healthy man to be as I to 5 of the entire weight of 

 the body. By experiments on the water-newt (lacerta palustris), he found the proportion in this animal to 

 be only as 2^ to 36. 



t Mr. Brande denies that iron exists more in the red particles of the blood than in the other principles • 

 according to his experiments, it exists but in a very inconsiderable quantity in any of them ; but he has 

 traced it in the chyle, in the serum, and in the fibrine, or washed crassament. Phil. Trans. 1812, p. 112 

 Vauquelin has traced it as a constituent in egg-shells and oyster-shells. Thomson's Annals of Philos 

 No. 1, p. 66. But Berzelius has proved Brande to be mistaken, and that iron exists largely in the blood, 

 and is the cause of the red colour. See his Anim, Chemistry. 



