[ 3 J 9 ] 
could find any point of dilution where the acids 
like the neutral falts produced no change on the 
figure of the vehicles. This experiment is the more 
to be attended to, as thefe vehicles have been fup- 
pofed to be oily and faponaceous, which is impro- 
bable, fince they difiolve more readily in acids than 
in alkalies. 
Salts made with earth of alum, and any of the 
acids, always corrugate thofe velicles, unlefs they 
be very much diluted ; when their effects are fi-- 
nrilar to thofe of the water alone, that is, they 
make the vehicles affume a fpherical fhape. I could 
not difcover any point of ftrength in thefe folutions 
where the particles would remain in them without 
being changed in their fhape. 
The fame was obferved of fpirit of wine: fome 
of the metalline falts, as copperas, iublimate, and 
Roman vitriol, were tried; and when much diluted; 
their effeds were not different from thofe of water; 
but in proportion as the folutioii was ftronger, they 
corrugated the veficles more and more. 
Urine, when containing much of its falts, has 
effeds fimilar to the ferum ; but in proportion as 
it is weaker, its effeds are more like thofe of 
water. 
The ufe therefore of thofe falts which enter into ' 
the compofition of the blood is probably to preferve 
the red veficles in their flat form ; for we muff 
fuppofe fome advantages attend that fhape, fince 
nature has made ufe of it fo generally in the blood' 
of different animals. And as both a very ftrong 
folution of neutral falts and a very diluted one alters 
the fhape of the veficles, it is probable nature has 
limited; 
