VOL. LXXXVII.] PHILOSOPHICAL TRANSACTIONS. 235 



I then put to another piece of the same crassamentum an equal quantity of serum, 

 and exposed both parcels to the atmosphere. The result was, that the blood in the 

 diluted urine did not become nearly so florid as that in the serum. I have found 

 also, that a solution of sugar in water conveys the influence of air to blood ; from 

 which it seems probable, that milk owes its similar property to the saccharine matter 

 which it contains. Black blood exposed to the atmosphere under mucilage of gum 

 arabic, does not become florid. 



It has been said, (Fordyce's Elements of the Practice of Physic, p. 14), that 

 neither serum, nor solutions of the neutral salts, dissolve the red matter of blood. 

 But this induction has been made from too small a number of experiments. For 

 saturate solutions of all the neutral salts, which I have tried, will extract, though 

 slowly, red tinctures from blood, some of which are very deep; and neither they, 

 nor serum, added in any proportion to a solution of the red matter in water, alter 

 its colour or transparency, except by diluting it. The following experiments how- 

 ever, will place this point in a clearer light. 



I added 1 dr. of distilled water to 1 oz. of serum, and poured the mixture on a 

 small piece of crassamentum. On an equal piece of crassamentum I poured 1 dr. 

 of water, and after some time added 1 oz. of serum. Each parcel therefore con- 

 tained the same quantity of crassamentum, serum, and water; but the crassamentum 

 on which the mixture of serum and water had been poured, communicated no tinge 

 to it; while the other piece, to which water had been first applied, and afterwards 

 serum, gave a deep colour to the fluid above it. I made similar experiments with 

 crassamentum, water, and a dilute solution of a neutral salt, which were attended 

 with the same results. 



Since then neither serum, nor a dilute solution of a neutral salt, will extract co- 

 lour from blood, though they are both capable of dissolving the red matter, when 

 separated by water from the other parts of the mass, it follows, in my opinion, that 

 what are called the red globules consist of 2 parts, one within the other, and that 

 the outer, being insoluble in serum or dilute solutions of neutral salts, defends the 

 inner from the action of those fluids. It is remarkable, that microscopical obser r 

 vations led Mr. Hewson to the same conclusion, viz. that the red globules consist 

 of 2 parts, (Hewson's works, vol.3, p. 17) which, according to him, are an exte- 

 rior vesicle, and an interior solid sphere. But the same writer, on the authority of 

 other microscopic experiments, asserts that the vesicles are red. If they be so, 

 there must exist 2 red matters in the blood, possessing different chemical properties; 

 which is certainly far from being probable. The exterior part of the globule appears 

 to be that ingredient of the blood on which common air and the neutral salts pro- 

 duce their immediate effect, when they render the whole mass florid; for I have 

 shown that they do not act on the red matter itself, and I have not found that they 

 occasion any change in coagulated lymph or serum. The only matter then which 

 remains to be operated on, is that which I have mentioned. It seems evident also, 

 from what has been just stated, that there exists an animal matter in the blood, 



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