on the Colour of Blood. 431 
open to the action of any solvent.* The addition, however, 
of a small quantity of a neutral salt to the water enables the 
vesicles to preserve their shape, and to retain the inner sphe- 
rules. -f Upon the addition of a greater quantity of salt, the 
vesicles contract, and apply themselves closely to the red par- 
ticles within. J Thus far Mr. Hewson’s observations extend. 
Let it now be supposed that the vesicles contract still more, 
from a further addition of salt to the water ; the consequence 
must be, that, as the internal particles are incompressible, the 
sides of the vesicles will be rent, and their contents exposed to 
the action of the surrounding fluid. Both water and a strong 
solution of a neutral salt may, therefore, destroy the orga- 
nization of the vesicles, though in different ways, and thus 
agree in bringing the red matter in contact with a solvent; 
while a mixture of those two fluids, namely, a dilute solution of 
a neutral salt, will, by hardening the vesicles, increase the de- 
fence of the red matter against the action of such substances 
as are capable of dissolving it. But all reasoning founded upon 
experiments with microscopes, ought perhaps to be regarded 
as, in great measure, conjectural. 
* Hewson’s Works a Vol. III. p. 17. 
f Ibid. p. 40. j Ibid. p. 31, 
