800 The Beneficial Influence of Plants. | December, 
inquiry only so far as relates to the effect of dry air at the ordi- 
nary temperature of such rooms. 
If an apartment is heated to sixty-five or sixty-eight degrees 
the air contains a much smaller proportion of vapor than if the 
air were warmed to the same degree by a stove or open fire-place. 
In this manner a great demand is made upon the system to sup- 
ply the air with moisture, the skin and pulmonary mucous mem- 
brane are dried, and a condition is induced which is expressed in 
irritability of the nervous system, paleness and susceptibility of 
the skin to cold, liability to pulmonary diseases, and, in a word, 
deterioration of all the functions. 
Now, it will not be doubted by any one, that if, as we have 
_ attempted to point out, the presence of a certain number of 
thrifty plants in an occupied apartment, warmed by dry air, would 
have the effect of raising the proportion of aqueous vapor to the 
extent indicated, plants in rooms heated by a hot-air furnace 
would in a hygienic point of view, be of very decided value, since 
they may become the means of obviating very distressing symp- 
toms, or even disease itself. Indeed, the circumstance of so 
large a portion of the population of cities and towns using the 
hot-air furnace as a means of heating their dwellings would seem 
to justify the conclusion that there is a connection between their 
bodily ills and this method of heating, that one might be trace- 
able, in part, to the other. It is true there are good uses of dry 
heat for the relief of certain diseases, but it requires a judicious 
application—a knowledge of the conditions in which it is indicated ; 
_ it should be employed only when prescribed by a regular physi- 
cian. In his very able paper, Prof. Pettenkofer wisely con- 
siders the impression which, plants (and plantations) make upon 
our mind and senses to be of hygienic value. And, furthermore, 
he says: “I consider flowers in a room, for all to whom they give 
pleasure, to be one of the enjoyments of life, like condiments in 
food.” May we not now rightfully consider plants kept in 
rooms under proper regulations to be of sanitary value also on - 
~ account of their influence over the proportion of vapor in the 
= air? And of the two effects is the latter not worthy of being 
made the paramount consideration ? ? 
1 Stillé Therapeutics, Vol. i, pp. 637-8. 
2 The following letter was received fr my estimable friend as an acknowledg- 
ment of ~ ETF. on the Transpiration of Plants, which appeared in the March 
