Schumburg and Zuntz also regard the increase of red blood corpuscles in
the higher mountains as relative only, but explain it by an altered
distribution of the corpuscular elements within the vascular system. In
their earlier work Cohnstein and Zuntz had already established that the
number of corpuscles in the capillary blood varies with the width of the
vessels and the rate of flow in them. If one reflects how multifarious
are the merely physiological influences at the bottom of which these two
factors lie, one will not interpret alterations in the number of the red
corpuscles without bearing them in mind. In residence at high altitudes
various factors bring about alterations in the width of the vessels and
in the circulation. Amongst these are the intenser light (Fuelles), the
lowering of temperature, increased muscular exertion, raised respiratory
activity. Doubtless, therefore, without either production of microcytes
or production _de novo_, the number of red corpuscles in capillary blood
may undergo considerable variations.

The opposition, in which as mentioned above, the views of Grawitz,
Zuntz, and Schumburg stand to those of the first mentioned authors,
finds its solution in the fact that the causes of altered distribution
of the blood, and of loss of water, play a large part in the sudden
changes. The longer the sojourn however at these great elevations, the
more insignificant they become (Viault).

We think therefore that from the material before us we may draw the
conclusion, that after long residence in elevated districts the number
of red blood corpuscles is absolutely raised. The therapeutic importance
of this influence is obvious.

Besides high altitudes, the influence of the tropics on the composition
of the blood and especially on the number of corpuscles has also been
tested. Eykmann as well as Glogner found no deviation from the normal,
although the almost constant pallor of the European in the tropics
points in that direction. Here also, changes in the distribution
occurring without qualitative changes of the blood seem chiefly
concerned.

* * * * *

The same reliance cannot be placed on inferences based on the results of
the Thoma-Zeiss and similar counting methods for anaemic as for normal
blood, in which generally speaking all the red cells are of the same
size and contain the same amount of haemoglobin. In the former the red
corpuscles, as we shall shew late