The mouth temperature of a healthy person is about 98.6° F. This statement holds true if the person has been sitting with his mouth shut for a little while before his temperature is taken; but a hot bath, breathing through the mouth, eating or drinking, and so forth may cause marked temporary changes.
The temperature in the rectum generally varies less than the temperature in the mouth unless it is taken when the rectum contains fecal matter. The temperature should be taken by rectum in babies and young children, restless, drowsy, or delirious patients, patients who cannot be trusted to keep the thermometer under the tongue, mouth breathers, and in any patients who have difficulty in keeping the mouth shut. The temperature is normally about half a degree higher in the rectum than in the mouth.
In order to take a temperature by rectum, adults generally find it more convenient to lie on the side and prefer, if they are able, to insert and hold the
thermometer themselves; but the attendant should be certain that they can do so without breaking the thermometer. Rectal thermometers should be lubricated with oil or vaseline before using; they should be inserted about two inches, left in three minutes, and cleansed in the same way as the mouth thermometer. A thermometer used to take rectal temperatures should never be used in the mouth.
In taking the temperature of a baby place him on his back, hold him firmly with his legs elevated, and carefully insert the bulb of the thermometer, well oiled, for about one inch. Keep the child quiet, and hold the thermometer in place three minutes. Great importance should not be attached to a slight fever of short duration. The temperature of a child is much more easily affected by slight causes than that of an adult, and rectal temperatures between 97.5° and 100.5° should not cause anxiety unless continued.
Temperatures taken in the axilla are less accurate than those taken by mouth or rectum. Consequently the method is less often used. The axilla should first be wiped; then the thermometer should be inserted and held for 5 minutes by pressing the arm tightly against the chest wall. The temperature in the axilla is normally about half a degree lower than in the mouth.
The temperature varies somewhat according to the time of day. It is not unusual for the mouth temperature of persons who are entirely healthy to be as low as 97° in the early morning, or as high as 99° in the late afternoon, and probably most people's temperatures vary as much as a degree during the twenty-four hours. Even greater variations that are not long continued have little if any significance in people who feel well.
Decided variations either above or below normal are highly important symptoms. A temperature below 98° is called subnormal, and one above 99.5° is called fever. The number of degrees of fever does not necessarily bear a direct relation to the severity of an illness. Thus, it does not follow that one person is twice as sick as another, because his temperature is twice as many degrees above normal. All symptoms, including variations in temperature, must be considered in connection with one another, and it is generally impossible to state the significance of any one symptom taken by itself.
The temperature should be taken once or twice a day as a matter of routine in almost every form of illness, and oftener when the patient's condition requires it. Also it should be taken as a matter of routine whenever there is indication of beginning sickness; especially when there is headache, pain,
sore throat, coated tongue, cough or cold, chill, vomiting, diarrhœa, or rash. It is not a good plan to take one's own temperature oftener than necessary, or indeed anyone's; certainly not a baby's, since frequent use of the thermometer may irritate the rectum.