f som J 
our celebrated countryman, the late Doétor Bryan Robinfon, T 
found fome facts and obfervations which appear to me to go a 
great way towards an explanation. 
In order to make thefe facts intelligible to perfons not very 
converfant in fuch fpeculations, I muft premife, that Dodor 
Prieftly has fully proved one great and indifpenfable ufe of refpi- 
ration to be to carry off or leffen a certain quality in the blood, 
which is known by the name of phlogifton. That this can only 
be done by pure air. That by the addition of phlogifton to 
blood it acquires a deep black colour ; and by its avolation, that 
blood returns to its natural ford hue. 
Now Doétor Robinfon found by experiment *, that the weight 
of the heart, in refpe@t to the weight of the body, is greater in’ 
children than in grown bodies, and that their quantity of blood is 
proportional to the weight of the heart. He found alfo, that the 
quantity of blood, which flows through the lungs in a given time, 
in proportion to the mafs of circulating fluids, is greater in children 
than in grown bodies; and that this proportion leffens continually 
from the birth till bodies arrive at their growth. Hence he re- 
marks, that as the blood of children paffes oftener through the 
lungs, it is more fluid and of a brighter colour than the blood of 
grown perfons. 
Ir this be a true picture of the conftitution of infants, we 
muft prefume that fuch peculiarities are intended to anfwer fome 
very 
* See page 13, et feq. 
