21G 
On the Composition of the Blood. 
bonic acid— this existing in the form of a per-ox'u]e in arterial, antT 
a prot.-<^xide in venous blood. More recent investigations have,, 
however, disproved this, which is known as the Liebigian theory, 
by showing that when the hoemato-globuline is liberated from 
the cells, it does not change its shades of hue by an exposure to 
the gases in question ; and further, that after all the iron is re- 
moved, its red colour still remains. 
The absorption both of oxygen and carbonic acid by the blood 
is found to produce a pht/sical change in the condition of the red 
cells. Thus by the influence of the first-named the cell-walls, 
are contracted or shrivelled, while ty the latter they are dilated 
or expanded. These alterations in form necessarily lead to an, 
alteration in the refraction of the rays of light, and it is now 
thought, that the bright-red hue of arterial and the dark hue of 
venous blood are mainly due to this simple cause. The action 
also of carbonic acid on the salts of blood contained within the- 
serum is said to have an influence in producing the Modena red 
colour. 
In concluding this part of our subject we may incidentally^ 
direct attention to the fact, that the inhalation of ether, chloro- 
form, and other similar anscsthetic agents, produces a dark- 
coloured blood, which is found under such circumstances to be 
flowing not merely through the veins, but the arteries also, and 
of necessity but imperfectly supporting the various functions ot' 
organization and life. 
We come now to speak of the only remaining constituent of 
the circulating fluid, which it is necessary to direct special 
attention to, namely— 
The White Corpuscles. — These bodies, although exceedingly 
numerous, are considerably less so than the red. It has beea 
computed that about one white to fifty red cells exists in a 
healthy state of the system, and in almost every other respect the 
white differ from the coloured cells. In size they exceed them 
for while the average dimension of the red cell is about the 
^gL_th of an inch, these measure as much as the 2b0(y Their 
iorm also is different, the white cells being globular-shapetl 
bodies and not flattened discs. Again, their contents are found 
to be granular when viewed with a microscope, which gives, 
them a dark dotted-like appearance totally unlike the red cells. 
Physiological anatomists are not agreed as to the origin and use 
of the white cells ; but by most they are regarded as identical with 
the cells which are met with in the chyle before this fluid is 
mingled with the blood proper : and certainly they would appear 
not to be essentially different from chyle cells when micro- 
scopically examined. Some have viewed them as ministering. 
