tant for physiology, pathology,
and therapeutics, and has come to the front especially in the last few
years, since Viault's researches in the heights of the Corderillas. As
his researches, as well as those of Mercier, Egger, Wolff, Koeppe, v.
Jaruntowski and Schroeder, Miescher, Kuendig and others, shew, the
number of red blood corpuscles in a healthy man, with the normal average
of 5,000,000 per mm.^{3}, begins to rise immediately after reaching a
height considerably above the sea-level. With a rise proceeding by
stages, a new average figure is reached in 10 to 14 days, considerably
larger than the old one, and indeed the greater the difference in level
between the former and the latter places, the greater is the difference
in this figure. Healthy persons born and bred at these heights have an
average of red corpuscles which is considerably above the mean; and
which indeed as a rule is somewhat greater than in those who are
acclimatised or only temporarily living at these elevations.

The following small table gives an idea of the degree to which the
number of blood corpuscles may vary at higher altitudes from the average
of five millions.

-------------------+---------------+-------------------+-------------
Author | Locality | Height above sea- | Increase of
| | level |
-------------------+---------------+-------------------+-------------
v. Jaruntowski | Goerbersdorf | 561 metres | 800,000
Wolff and Koeppe | Reiboldsgruen | 700 " | 1,000,000
Egger | Arosa | 1800 " | 2,000,000
Viault | Corderillas | 4392 " | 3,000,000
-------------------+---------------+-------------------+-------------

Exactly the opposite process is to be observed when a person accustomed
to a high altitude reaches a lower one. Under these conditions the
correspondingly lower physiological average is produced. These
interesting processes have given rise to various interpretations and
hypotheses. On the one hand, the diminished oxygen tension in the upper
air was regarded as the immediate cause of the increase of red blood
corpuscles. Miescher, particularly, has described the want of oxygen as
a specific stimulus to the production of erythrocytes. Apart from the
physiological improbability of such a rapid and comprehensive fresh
production, one must further dissent from this interpretation,