372 
POPULAR SCIENCE REVIEW. 
meter firmly in the right hand, bulb downwards, and gently 
tapping the one hand against the other. After four or five 
taps the index will be seen to have descended a certain number 
of degrees, and when its upper end has descended below 96° F., 
it has been sent down sufficiently far. Great care must be taken 
not to shake the thermometer so violently as to make the index 
go into the bulb. 
After the register has been properly adjusted at about 96°, it 
is better to hold the bulb in the hand for a few minutes before 
first using it, so as to raise the temperature of the whole mass 
of the mercury. And in doing this, it does not matter in the 
least if the index is by this means pushed up above 97°, for it is 
a certain fact that the temperature in the closed hand never 
exceeds that in the mouth. 
The floor of the mouth is the only suitable place in which to 
determine the temperature of the body ; for though it may not 
indicate quite as high temperature as deeper parts, nevertheless 
it very nearly does so, and gives indications of the least change 
in the body temperature with great accuracy. It is necessary 
for this that the mouth should be kept closed for a short time 
before an observation is made. The thermometer, warmed as 
above directed, is then placed in the mouth, as far back as 
possible below and to the side of the tongue, and retained there 
for two and a half or three minutes. Then, without opening 
the mouth, or withdrawing the instrument from it, the bulb is 
transferred by the stem to the other side of the tongue, and 
retained there for the same time. The thermometer may, at the 
end of the five minutes, be withdrawn, and the height of the 
index recorded, the time at which it was taken out being indi- 
cated at the same time. 
In observations like some to be recorded further on, when 
the temperature is taken every five minutes, the instrument, 
immediately after having been read off, is shaken down and 
replaced in the mouth, the record for one time being kept whilst 
the temperature for the next is being obtained. 
The source of the internal body-heat must now engage our 
attention, and the argument from analogy will assist in ex- 
plaining it. A fire is warm because of the chemical decom- 
position, or degradation, which is occurring in its fuel. Under 
the influence of the oxygen of the atmosphere the elaborate 
hydrocarbons are being reduced to the condition of carbonic 
anhydride and water. A boiler on the fire may drive a steam- 
engine. The heat imparted to the water in the boiler is the 
source of the power of the engine, which latter depends for its 
working properties on the difference between the temperature 
of the steam and that of the condenser in the low-pressure, 
or the external air in the high-pressure engine. The machine 
is a heat-engine. 
