175 
by Apjohn’s formula is higher than what I have obtained 
with other instruments this winter. I hear that some im- 
portant experiments are now being made on various hygro- 
meters, and we may hope that they will result in bringing 
about greater uniformity than now exists. 
Dryness of Air we breathe. 
Although it is necessary that the meteorological condi- 
tions of the air should be studied, we must not stop there, 
but must afterwards find what is the influence upon the 
human organism. I formerly pointed out how much pa- 
tients could be out of doors in Davos, and extended expe- 
rience convinces me that they enjoy, in favourable winters, 
more fresh air out of doors than in warmer resorts, as the 
Riviera ; but this time I will not stop there, for what is also 
very important, we can enjoy fresh air more in our rooms 
than in most warm resorts. No doubt it will at first sight 
seem strange that consumptive patients should sleep with 
their windows open* where the temperature is 10°, 20°, 
30° F., or even more, below freezing point ; but consideration 
wi]l show that it is only reasonable and what we might 
expect, for with the low temperature the absolute amount 
of moisture, even were the air saturated, could be but small. 
Now the cold air entering into the room is rapidly warmed, 
and as the amount of moisture it contains is a very small 
proportion of what air at the room temperature can contain, 
this causes the relative moisture of the room to be very low. 
I have found this winter that in my room this percentage 
of the possible moisture has varied from 25° — 35° as mea- 
sured with a hair hygrometer and also with a Regnault’s 
condenser hygrometer. As an example, on January 15th, 
at 9 a.m., the temperature of the air out of doors was 18° F, 
* When I speak of the window being open I do not mean wide open, 
but one large pane or the top of the window open, and this is enough to 
keep the air fresh. Much wind prevents this, but fortunately this has 
been very rare this winter. 
