FORESTS AS SITES FOR SANATORIA 25 
tions are so dilute that their effect is more psychical than 
physical” is not scientific. 
Most people write of the turpentine emanations of pine 
forests, but the large amount of resin and turpentine stored 
in the wood and bark of the stems and branches is not 
exhaled into the atmosphere, except in the case of wounds 
or disease of the trees, which cause a flow of resin. The 
odour of pine woods is due, in great measure, to a volatile 
oil contained in the leaves. This is variable in composition, 
containing pinene (the main or often sole constituent of 
turpentine oil), sylvestrene, phellandrene, and a notable 
percentage of bornyl acetate, which gives to it a character- 
istic odour. Pine-needle oil, produced by distillation, is a 
clear odourless fluid used as a deodorant in baths, hospitals, 
etc., and is sold all over the world for rheumatic com- 
plaints (9). 
No scientific study of the odours of the air from a 
therapeutic point of view has, I believe, ever been attempted. 
We are, moreover, quite in the dark as to the curative effect 
of change of air in many cases of illness, which is in our 
ignorance ascribed to psychic causes. 
Two suggestions have been made in explanation of the 
curative effects of the odours of pines on tubercular diseases 
of the lungs. Dr. Horace Dobell relied on Kingzett’s ex- 
periments (10) on the oxidation of volatile oils under the 
influence of air and moisture, when peroxide of hydrogen 
and camphoric acid were produced, the former being a 
powerful disinfectant and the latter an antiseptic. The 
volatile oil exhaled by pines being converted into these 
agents was supposed to render the atmosphere destructive 
to bacteria. No such germicidal action of the air in pine 
forests has, however, been proved to take place; and Dr. 
Dobell’s theory is no longer tenable. 
The researches in phagocytosis carried on by Prof. 
Hamburger (11) of Groningen University, Holland, possibly 
afford an explanation of the therapeutic effects of the odours 
of pine forests. He exposes on slides under the micro- 
scope drops of blood which have been put into various 
