PRECAUTIONS DURING AND AFTER BLEEDING. 147 



The low or even negative blood pressure in the jugular vein 

 renders it specially convenient for venesection, but at the same time 

 entails a certain danger of air being aspirated into it, with possibly 

 a fatal result. Usually, even if the vein be not compressed below 

 the incision, sufficient blood flows from above to preserve a slight 

 positive pressure. But a deep inspiration may be followed by so 

 rapid a rush of blood towards the heart as dangerously to favour 

 the indraught of air through the wound. This is not a frequent 

 accident, and it cannot well occur while the escaping stream of blood 

 is strong and full ; though it may happen after the stream slackens 

 or ceases. Compression of the vessel above the wound, as sometimes 

 happens from the patient leaning against the manger or on the 

 collar shank, is favourable to the aspiration of air through the 

 wound. For this reason the cutaneous wound should always be 

 sutured. 



The sudden or rapid entrance of a large volume of air into the 

 jugular is accompanied by a hissing, gurgling, or sucking sound at 

 the wound, followed by intense dyspnoea, dilated pupils, pallor of 

 the mucous membranes, and a peculiar churning noise which is heard 

 over the heart ; at once the horse staggers or sways to and fro, falls 

 to the ground, and may die in a few minutes. At one time insuffla- 

 tion of air into the jugular was frequently resorted to in destroying 

 horses. The vein was opened with a knife, a cannula or pipe-stem 

 inserted, and the operator — of good lung capacity — with his mouth 

 applied to the tube, blew as strongly as possible, the horse falling 

 and dying without a struggle. The mechanism of death from aspira- 

 tion of air into a vein has not been satisfactorily ascertained. It 

 has been supposed that the spumous or frothy mixture of blood 

 and air produces distension and paralysis of the right side of the 

 heart and consequent arrest of the circulation. 



Sufficient blood having been taken, the skin is closed either with 

 a pin or interrupted suture. In the former case the pin is cautiously 

 removed in thirty -six to forty-eight hours, the parts being supported 

 with the fingers of the left hand whilst those of the right rotate and 

 remove the pin. In closing the wound care must be taken not to 

 exercise much traction on the edges, as this might cause separation 

 of the skin from underlying tissues, and extensive extravasation. 

 Similarly, if during bleeding the outer opening be obstructed, blood 

 accumulates under the skin. Such extravasation would be of little 

 consequence were it not that by compressing the vein it may lead 

 to thrombus formation, and that it always supplies a favourable 

 medium for the further development of the micro-organisms which 



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