292 SHEA AND LAWSON, ON POPULAR PHYSIOLOGY. 
the liquid in which they float. The colour of the blood may even be 
altered by a change of form in the corpuscles. Thus it is probable that 
the difference in colour of arterial and venous blood depends on an 
altered form of the corpuscles contained. When subject to the action 
of water, corpuscles swell, become convex, or even round, and may at 
length burst. 
“With regard to the structure of red blood-corpuscles, they may be 
considered to be cells, provided with an elastic cell-wall, enclosing appa- 
rently homogeneous contents impregnated with red colouring matter, 
called hematine. The white corpuscles, however, seem to contain gra- 
nular matter, the cell-wall being scarcely ever visible unless the cor- 
puscles are treated with water or diluted acid, when the cell becomes 
distended, and the wall separated from the enclosed matter. 
“If the minute vessels in the web of a frog’s foot are examined, both 
varieties of blood-corpuscles will be seen hurrying along in the current 
of the blood, the red moving rapidly in the centre of the stream, the 
white passing more slowly along the sides of the vessels. 
“The functions served by the blood-cells have not been determined, 
nor has it been ascertained how or where they are formed. The most 
probable source of their origin is, that they are formed from the chyle 
and lymph corpuscles poured into the blood from the thoracic duct; as in 
the general current of the blood, corpuscles in intermediate stages of 
development are always found, and indeed, occasionally the fluid in the 
thoracic duct has a red tinge, supposed to be due to the commencing 
development of hzmatine in the interior of the chyle-corpuscles. _Doubt- 
less the blood-cells are continually undergoing decay, whilst others are 
being generated to supply their place; and most likely they are derived 
in the manner just noticed, for they are proved not to be developed by 
fission of the pre-existing corpuscles. 
“Chemically, the blood may be regarded as an alkaline fluid, com- 
posed principally of water, containing a certain amount of solid matter. 
Amongst the more important components of the solid matter, hematine 
may be mentioned. It is stated to contain iron, and is found mixed with 
globuline, the compound being termed eruor. 
Chemical Composition of the Blood. 
Water? ys Settee palin ete area 795 
Hematine... 8 
Blood Corpuscles_ ...4 Globuline ... 140 
bi) prc ee 1 
(Solid matter ...... METIS ea Sees cstecteacs 2 
miliaris ke he ee 40 
BAU 7 MAP, oe hia sh She ecsusec satan 2 
UADURUSs Rahs “oda nhac sa eeeee 8 
| Extractive matter ............ 4 
1000 
“The difference between venous and arterial blood, as regards colour, 
has been already noticed; but other differences exist; thus, in the arte- 
rial fluid there is less albumen and more fibrine than in the venous. 
Moreover, the specific gravity is lower, the amount of red corpuscles 
grater, and probably, the proportion of oxygen larger in the arterial 
ood. 
