Physiology and biochemistry in modern medicine . ). To be more exact, we may state that the removal of 5 of blood perkilogram of body weight does not influence the blood pressure. The re-moval of a second portion of 5 per kilogram causes the blood pres-sure to begin to fall, the fall of pressure for each subsequent 5 of 138 THE CIRCULATION OF THE BLOOD blood per kilogram removed averaging about 6 mm. Hg, until after 20to 25 of blood per kilogram have been removed, when a more rapidfall in pressure sets in (Downs*). When the pressure reaches the levelof from 20 to 30 mm. Hg,
Physiology and biochemistry in modern medicine . ). To be more exact, we may state that the removal of 5 of blood perkilogram of body weight does not influence the blood pressure. The re-moval of a second portion of 5 per kilogram causes the blood pres-sure to begin to fall, the fall of pressure for each subsequent 5 of 138 THE CIRCULATION OF THE BLOOD blood per kilogram removed averaging about 6 mm. Hg, until after 20to 25 of blood per kilogram have been removed, when a more rapidfall in pressure sets in (Downs*). When the pressure reaches the levelof from 20 to 30 mm. Hg, the danger limit is reached, for there nowsupervenes a train of symptoms known as shock, and the chances for theanimals recovery become uncertain. That the removal of the first por-tion of blood, if this removal is slow enough, does not influence the bloodpressure, indicates that some adjustment has occurred in the vascularsystem to hold up the pressure in spite of the loss of blood. This adjust-ment is believed to consist in Time mSees &.Abscissa Fig. 30.—The effect of rapid and slow hemorrhage on the arterial blood pressure. Betweenthe second and third pieces of tracing an interval of two minutes elapsed. Recovery from liemorrhage is remarkably rapid, the original volume ofblood being restored within a few hours. The chances of recovery de-pend upon the amount of blood lost, A loss equal to 2 or 3 per cent ofthe body weight can almost always be recovered from in laboratory ani-mals, and in the case of man there is reason to believe that recoverymay occur after as much as 3 per cent of the body weight has been recovery of blood pressure is brought about partly by a transferof fluid from the tissues to the blood. This abstraction causes a dryingout of the tissues, which soon excites an extreme degree of thirst! Thedilution of blood by fluid derived from the tissues occurs very rapidly,as can be shown by comparison of the hemoglobin content, or the
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