302 The Beneficial Influence of Plants. [ December, 
is well known that the property of transmitting light is possessed 
by bodies in different degrees; their ability to transmit heat has 
been found to be equally diverse. Now the diathermancy of sub- 
stances is greatly influenced by certain conditions, among which 
may be mentioned, more particularly, the nature-of the molecules 
of the body, its thickness, and especially the source or kind of 
heat. The rays which are not transmissible through a body are 
absorbed by it, thus elevating the temperature of the body ; when 
the body is perfectly diathermic, however, there is no elevation 
of temperature. Now, since the absorption and radiation of heat 
are reciprocal, it is interesting to know how the atomic constitu- 
tion of the body is affected in these processes. The rays on 
striking a body are some of them absorbed and heat the atoms of 
the body, when each of these atoms acts as a heated body itself, 
and emits the rays absorbed, in all directions. It has been proved 
that absorption does not take place on the surface, but within the 
absorbing body, a certain thickness being necessary to effect the 
phenomenon. 
As the substance with which we are most concerned is in the 
gaseous state—aqueous vapor in the air—we shall pass to the 
consideration of the radiation and absorption of gaseous sub- 
stances. When we reflect that some solid and liquid bodies are 
almost or entirely diathermic, it would, at first sight, appear 
absurd to talk of gases absorbing and radiating heat. One would 
sumptive patients; but I have never heard any physician advise that plants. should be 
placed in the sick chamber as a remedial measure. I hope your experiments will lead 
to a change of opinion on this subject—a change which you seem to anticipate—for if 
the exhalation really be so great, we have it in our power to regulate the amount of 
moisture in the sick room. Year after year new health resorts are urged on the 
public; abroad there are many; and in this country, from St. Augustine to Minne- 
apolis, they are to be found in every State, the low, warm, moist places of the - 
South, the cool mountain regions of the Middle States, and the cold, dry climate of 
Minnesota. Consumptives rush to every new place only to find, in a short time, that, 
like the others, it must be given up as useless. Science ae no influence in the choice 
of places. Allow me to speak of a case which in this connection may interest you. 
mother, her two sisters and only brother all died of consumption under fifty 
father’s side there was not a taint of any disease, but great 
strength and vigor. ne the children of my mother’s sisters and brother, though they 
lived to a good age and oyes good health, finally died of consumption. , Three of 
my brothers, acti ergetic men until within a few years of their death, died of 
= consumption at the ag ages of 55, 57 and 78 respectively, and a sister died of the same 
disease at 66. I mention these cases to show that the germs of the disease were 
: he the family. Thirty years ago my eldest sister, then above fifty years of age, 
