252 
PARK AND CEMETERY. 
STREET TREEvS, 
Trees have a sanitary effect upon cities. They 
serve to equalize the temperature, reducing it in 
warm weather, and raising it during cold. They 
cool the lower stratum of air during warm periods. 
They purify by utilizing certain gases no.xious to 
man and setting free other elements beneficial to him. 
Obliterating the forests and covering the earth’s 
surface with stone, brick, tin, etc., disturbs the 
natural forces in a manner detrimental to human 
life. The e.xistence in a city of arboreous vegeta- 
tion is of greater value than that of herbs or shrubs 
by reason of the much greater leaf surface exposed 
than occurs with the latter. 
Trees in health and performing their normal 
functions while exposed to the light, take carbon 
dioxide from the air. The carbon becomes fixed 
as the woody fibre, and oxygen is set free. To 
man, oxygen is a beneficial part of the air he 
breathes. Carbon, a waste product of man is 
injurious to him. Therefore it may be said: 
1. Trees purify the atmosphere. 
Transpiration is a normal function of vegeta- 
tion. Moisture from the soil is taken up by the 
roots and distributed in the tree. In the process 
of conduction and assimilation of food, incident to 
growth, moisture is liberated in the form of vapor. 
Vaporization cools as is illustrated by ether. 
Consequently, it may be concluded that: 
2. Trees act as a refrigerant. 
Nutritious soil, in a mechanical condition 
favorable to tree growth and provided with a 
suitable source of moisture, enables a growing tree 
to transpire more freely (within certain limits,) 
the higher the atmospheric temperature rises. 
I'ollowing this condition we may say: 
3. The refrigerant power of growing trees 
tends to increase with the rising of atmospheric 
temperature. 
The moisture taken up by the warm atmosphere 
during evaporation causes a diffusion in the air of 
a medium which prevents the escape of heat from 
the earth, consequently: 
4. Trees prevent solar irradiation from the 
earth. 
By their shade, trees protect the earth from the 
direct rays of the sun. This tends to prevent the 
earth from reflecting heat and rapid drying, and 
to prolong the period during which surface water 
is evaporated. 
During all seasons, trees maintain a mean 
temperature of 54 F. 
If the atmospheric temperature is 67 F. or 
above, the temperature of the tree is the lower, 
but if below 67 that of the tree is the higher. It 
follows that: 
5. Trees are equalizers of temperature and 
humidity. 
Contrasting the above statements concerning 
trees, are the following concerning conditions 
peculiar to urban life and man. It is hoped that 
together they will present sufficient evidence to 
clearly demonstrate the truth of the abstract 
statement occasionally made that trees are of a 
sanitary value to city folk. 
The mean normal temperature of man when in 
health is 98.6 F. A part of the heat generated by 
the body is converted into force. Some is lost by 
evaporation, radiation, and transmission to other 
bodies. Should the surrounding temperature be 
unduly increased, that of the body adjusts itself by- 
added expenditure; should it be less, added heat 
is generated by the body. 
An inherent constitutional power of man adjusts 
the temperature of the body so that whate\ er the 
atmospheric temperature may be: 
1. The mean temperature of the healthy body 
is 98.6. The extremes of variation in temperature 
of a healthy person are from 97.25 to 99 50. 
If the air is dry a person may endure for very^ 
brief periods, a temperature of 200 and even more. 
But if under such circumstances a rapid evaporation 
and radiation is impeded the temperature of the 
body would rise and threaten, or actually cause 
death. Any rise of temperature above the normal 
in man involves danger to human life. Therefore: 
2. Abnormally high temperature in the human 
body is dangerous. 
3. Sometimes it is dangerous to have the loss 
ofheat from the body impeded. 
In addition to direct solar heat there are nu- 
merous sources which contribute to the rise of 
temperature. Besides that from the human body 
the principal are fires from dwellings and factories. 
Hence: 
4. In the summer artificial heat tends to raise 
the atmospheric temperature to an unwholesome 
degree in cities. 
During warm weather the putrefaction of 
vegetables and animal matter, and liquids is rapid 
and their gases when in contact with the blood 
tends to create heat. Eating, drinking and breath- 
ing are the means of their entrance into the body. 
Death is one of the serious results of excessive 
heat, other and potent, though usually less serious 
results are visited upon the human being. They are 
sunstroke, abdominal affections, emaciation, deviti- 
lization and various chronic diseases. Therefore: 
(4) A warm ( i. e. , above 60 F.) temperature 
causes a rapid decomposition of certain matter, the 
gases of which when introduced into the blocd 
generate heat. 
