970 
Again, from this it is evident once more, that the observed formula 
of the white blood corpuscles in the circulating blood gives but a 
very inaccurate idea of the manner in which they can occur in 
the whole of the vascular system. Only those white blood cells 
which are carried along with the blood, flow out of the finger and 
the veins of the ear. A considerable part will however be retained 
to a greater or lesser extent in the capillary region where there is 
a very great surface action. 
A slight stimulus, such as the injection of a practically harmless 
fluid, in the abdominal cavity can cause a strong increase of that 
adhesion locally, and in this way, this adhesion after a few repeti- 
tions of the injection has the effect of sifting the blood free from 
white blood corpuscles in the capillaries of the abdomen. To a small 
degree this will undoubtedly always take place normally. In this 
local accumulation it comes to an increase of cells through division 
and besides, to a differentiation, in other words to a temporary, 
movable organ for the forming of different kinds of white blood 
corpuscles. This organ then owes its origin to the same extent to 
both blood and connective tissue. By looking at things in this light 
we could regard the bone-marrow not only as the factory of blood 
elements which are delivered into the blood; we would be equally 
justified in saying the reverse, namely that the elements of the 
blood are constantly attracted in the capillaries of the bone-marrow 
as a continuation of what takes place in the formation of bone in 
the embryo. In this way a tissue will arise that, in its turn, 
rejuvenates the blood, so that we have here the eternal process of 
reversion and equilibrium which we always find in the functions of 
the living cell. 
We can expand the subject still further; from the moment that 
the blood is formed in the embryo there arises an indisputable sepa- 
ration between tissues and blood which makes itself evident by the 
difference in quantity of albumen, and the difference in the nature 
of the cells. As an utterance of this contrast we f.i. find that the 
polynuclear cells which belong normally to the blood cannot exist 
in the tissue fluid. But on the other hand there undoubtedly is an 
attraction between the two elements, and this reveals itself especially 
in the capillary areas; there the difference is less pronounced and 
there also cellular and dissolved substances are interchanged. We 
could say that blood and tissue have a separated existence, have so 
to say opposite charges. 
Consequently the cells that wander in the blood always have an 
