The Changes in Clotting Power of an Oxalated Plasma on Standing

Howell1 has shown that in testing blood to determine the presence of a hemophilic tendency, it is more satisfactory to obtain the clotting time of the oxalated and centrifugalized plasma after recalcification than to depend upon the time of coagulation of the whole blood, since in the latter case small variations in conditions may make large differences in the figures obtained. In connection with this procedure and also as a matter of general interest, it was thought desirable to ascertain to what extent the coagulating property of an oxalated plasma undergoes alteration upon keeping, and the effect upon this property of temperature and of sterile versus non-sterile conditions. The following experiments were made at the suggestion of Dr. W. H. Howell with the object of testing these points. It is evident that determinations of the clotting time of blood kept over a period must be made upon oxalate or fluoride plasma. In these experiments, therefore, the following method was adopted: A cannula was introduced into one of the carotid arteries of an anesthetized cat, and the blood allowed to flow into centrifuge tubes containing one part of 1 per cent sodium oxalate for every eight parts of blood. The blood and oxalate were thoroughly mixed and then centrifugalized for twenty minutes. The cell-free plasma was pipetted off and divided into three parts, one of which was kept at 4°C. during the period of the experiment, another at room temperature and the third at 37’. The clotting time of these specimens was determined at intervals over a period of twenty-four hours by the method of recalcification. It is well known that if calcium be added to a plasma kept fluid by oxalate precipitation of its ionizable calcium the plasma will readily coagulate, the rapidity of coagulation being determined by the