COLOURLESS CORPUSCLES—USES OF RED CORPUSCLES. 209 
mode in which this reproduction is effected has not yet been 
_ clearly made out ; but there is strong reason to believe that the 
red corpuscles are developed from the corpuscles of the chyle 
and lymph (§ 222) which are continually being poured into 
! the ci ing current, and of which isolated examples, known 
_as the white or colourless corpuscles, are met with in every 
_ drop of blood that is examined under the microscope. The 
_ size of these is pretty much the same in all Vertebrata, their 
_ diameter being usually about 1-3000th of an inch. In the 
_ blood of Man and the Mammalia in general (fig. 115, p) they 
are not easily distinguished from the red particles; their 
_ diameter being nearly the same, while the colour of single 
dises of the two kinds is not very dissimilar. But in the lower 
_ Vertebrata, whose blood has large oval red particles, the differ- 
ence between the two kinds is very obvious ; and the resem- 
blance which the colourless globules (c, figs. 116-119) bear to 
those of the chyle and lymph, is very striking. Similar colour- 
less particles exist, to a variaole amount, in the nutritive fluid 
of Invertebrated animais; so that in this, as in some other 
 Tespects, that fiuid bears a stronger resemblance to the chyle 
and lymph of the Vertebrata, than it does to their blood, 
which is characterised by the presence of the red particles. 
235. Physiologists are now generally agreed, that one of 
the functions of the Red Corpuscles is to convey oxygen from 
the lungs to the tissues and organs through which the blood 
circulates, and to bring back the carbonic acid which is set 
free in these, so as to deliver it at the lungs. For although 
it is certain that the liguor sanguinis can also convey these 
gases, yet experiment shows that the red corpuscles can take 
up, bulk for bulk, a much larger proportion of them; and 
that the blood which is richest in these particles is, therefore, 
“most fit to serve as the medium for the transmission between 
the respiratory organs and the body at large. Now it is in 
the nervo-muscular apparatus that there is the greatest demand 
for oxygen; for this apparatus is not capable of vigorous 
action, unless oxygen be freely supplied to it. The quantity 
of this it requires, however, depends upon the exercise of its 
‘powers ; for when at rest, it needs little or no more than is 
made use of by the other tissues ; but whilst in activity, it 
needs a greatly-increased supply. The quantity of oxygen. 
ich the animal takes-in by its lungs, and the amount of 
P 
