To obtain any reliable data from the pulse it must be felt during perfect quiet. During sleep is the best time, but if the child cannot be caught in this condition, advantage may be taken of its placidity while feeding or amused by a toy. With very young infants it is sometimes impossible to feel the beat of the artery at the wrist, and it is necessary to ascertain the frequency of the pulse by listening to the heart. After the second month feeling the pulse at the wrist in the ordinary way is not difficult.

The child's pulse differs from the adult's in being much more frequent, more irregular, and more irritable.

The frequency, or the number of beats per minute, varies with the age. The following is the average rate:

From birth to 2d month...............

160 to 130

From 2d to 6th month................

130 to 120

From 6th to 12th month..............

120 to 110

From 1st to 3d year..................

110 to 100

From 3d to 5th year..................

100 to 90

From 5th to 10th year................

90 to 80

From 10th to 12th year...............

80 to 70

These figures represent the pulse in a waking, but passive state. During sleep the frequency is less. Thus, between the second and ninth years there are about sixteen beats less per minute while asleep than when awake; between the ninth and twelfth years, eight less; and between the twelfth and fifteenth years, only two less. Below the age of two years the disparity is even greater.

The irregularity of the pulse in childhood is confined to an alteration of the rhythm, in other words, of the intervals at which the beats succeed each other and the relative strength and volume of each beat. It is most marked in infants and is greatest during sleep, when the pulse is lowest.

The feature of irritability, that is, the facility with which the frequency is increased by muscular activity and mental excitement, is greater in proportion to the youth of the child. A rise of 20, 30, or even 40 beats a minute is not uncommon in early infancy, under the excitement of the slightest effort or disturbance.

Examples of Variations in Disease. - On account of the wide variations in health, little meaning need be attached to alterations of the rhythm and frequency while unassociated with other abnormal features. When so associated they become important in determining the existence of disease.

Increased frequency is a constant attendant of the febrile state. The extent of the increase corresponds with the degree of elevation of temperature, though the pulse curve always runs higher than the temperature curve. As a rule, the more frequent the pulse the higher the fever. In estimating the risk of the increase, however, the law of the fever in question must be taken into consideration. For example, in scarlet fever a pulse of 160 is usual and not indicative of special gravity. In measles, the same degree of acceleration would be abnormal and show great danger.

Jaundice and inflammation of the kidneys are accompanied by a diminution of the pulse rate.

Irregularity is met with in diseases of the brain and heart, and sometimes in nervous and blood-impoverished children.