4^0 Dr. Wells’s Observations and Experiments 
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 ob- 
servations led Mr. Hewson to the same conclusion, namely, 
that the red globules consist of two parts,* which, according 
to him, are an exterior vesicle, and an interior solid sphere. 
But the same writer, upon the authority of other microscopic 
experiments, asserts that the vesicles are red. If they be so, 
there must exist two red matters in the blood, possessing dif- 
ferent chemical properties ; which is certainly far from being 
probable. 
The exterior part of the globule appears to be that ingre- 
dient of the blood upon which common air and the neutral salts 
produce their immediate effect, when they render the whole 
mass florid ; for I have shewn they do not act upon 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 upon, is that which I have men- 
tioned. It seems evident also, from what has been just stated, 
that there exists an animal matter in the blood, different from 
the coagulable lymph, the coagulable part of the serum, the 
putrescent mucilage, and the red particles, which, I believe, 
are all the kinds it has hitherto been supposed to contain. 
The microscopical observations of Mr. Hewson appear like- 
wise to furnish a reason, why both water, and a saturate solution 
of a neutral salt, can extract colour from the red globules, 
though a mixture of those fluids be incapable of the same 
effect. For water applied to the red globules, separates the 
exterior vesicles from the red particles, which are therefore now 
* Hew son’s Works, Vol. III. p. 1 7. 
