In children, and occasionally in others, where the veins of the arm are small and undefined, blood is drawn from the external jugular veins. As this operation would only be performed by a surgeon, it is unnecessary to describe it; and we will merely remark, that as the entrance of air into the vein during the operation, or until the orifice of the vein has been closed, would cause instant death*, this vein should only be opened in extreme cases.
We have no space to notice at any length the general results of bleeding, or the much disputed question, whether venesection should not be discarded from our list of opera tious,f because no rational doubt can be entertained that, although, until a quarter of a century ago, or later, there was a most unnecessary and probably hurtful effusion of blood, venesection, in properly selected cases, is one of the most valuable remedies. A patient can bear a much greater loss of blood in the horizontal position than when sit ting, and in that position than when standing. The condition required.to be produced is
that there should be incipient faintness; and the loss required to produce this effect varies extremely in different individuals and in different diseases. The late Dr. Marshall Hall, in his work on The Effects of the Loss of Blood, states that the average loss of blood required to produce slight faintness in a healthy person in the sitting position is 15 ounces. In some diseases, more, and in others less, than this loss can be borne. The greatest loss can be borne in congestion of the head, or tendency to apoplexy (from 50 to 40 ounces); then in inflammation of the serous membranes and of the parenchymatous substance of various organs (from 40 to 30 ounces); then acute anasarca (about 20 ounces); and then inflammation of the mucous membranes (about 16 ounces); while the system bears less than the quantity borne in health, in the eruptive and other fevers, in delirium tremens, dyspepsia, and chlorosis—a set of diseases in which blood-letting is now scarcely ever resorted to.