CHANGES IN THE BLOOD, 101 



Bisted upon, that the course of treatment is to be guided hy 

 the condition of the pulse, then the withdrawal of blood would 

 be contra-indicated in every instance. But practitioners who 

 hfive thought over the matter know full well that a moderate 

 bleeding is followed by a diminished acceleration of the pulse, 

 and unprovement in its tone, and that many congestions are 

 immediately relieved by such procedure. The explanation is 

 not difficult. In cerebral congestions the diminished cardiac 

 power and feebleness of the pulsations are caused by the 

 pressure of the congested vessels upon the brain substance: 

 in many instances this pressure is increased by the transudation 

 of serum from such congested vessels. By diminishing the 

 brain pressure by the abstraction of blood, the cause of the 

 debility is at once removed. The heart is now able to beat 

 fully and strongly, and thus a small, feeble, or even thready 

 pulse is changed into a full, soft pulsation. The variety of 

 opinions held as to the possibility of causing an alteration of the 

 fluids within the cranium by bleeding or otherwise, need not be 

 discussed at present. My own experience leads me to the con- 

 clusion that a cofliatose condition produced by cerebral or 

 cerebro-meningeal congestion is often removed, the pulse being 

 at the same time improved in tone, by a moderate bleeding. 

 Pulmonary congestion find the feebleness of the heart's action — 

 the " oppressed action " as it has been termed— are aggravated by 

 the right side of the heart and the great veins being choked with 

 blood. In this instance, it is true, the withdrawal of blood 

 does not reheve by removing the primary cause — that is, 

 the congestion of the pulmonary capillaries — but, a most im- 

 portant complication, it diminishes the supply of blood to the 

 already overloaded heart, and through it to the already con- 

 gested vessels. Bearing this in mind, the rapidity with which tlie 

 withdrawal of a large stream of blood produces an impression will 

 be understood ; indeed,, it can most truly be stated that the relief 

 afforded does not depend so much upon the quantity withdrawn, 

 as upon the rapidity of the withdrawal. For example, six or eight 

 quarts of blood might be abstracted in a small or trickling stream, 

 and afford no relief, but, on the contrary, do much harm, by 

 causing debility or exhaustion ; but a smaller quantity, if 

 withdrawn rapidly, may be followed by a marked remission of all 

 the distressing symptoms. In the one case, the blood supply tj 



