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A previous report from this laboratory (1) presented the results of hematologic studies in nine dogs cooled below 200 C. During induction of hypothermia the animals showed a marked rise in red cell count, hemoglobin, and hematocrit, together with a nearly complete disappearance of white cells and platelets. On rewarming, the values all returned to normal. A number of studies have been carried out to learn more about the mechanism of these changes. The present paper describes some of the studies dealing especially with the changes in platelets and white cells. MATERIALS AND METHODSThe experiments were performed on a group of 22 adult mongrel dogs. Hypothermia was induced by a method of surface cooling previously reported (2). Each dog was anesthetized with intravenous thiopental. An endotracheal catheter was inserted and connected to an automatic respirator utilizing room air. Thermocouples in the rectum and esophagus permitted continuous temperature recordings by a Brown potentiometer. A continuous three limb lead electrocardiogram and aortic blood pressure were also recorded. The animal was placed in an ice bath at 40 C. and cooled until ventricular fibrillation occurred or the rectal temperature reached 170 C. The heart was defibrillated electrically.Each experiment, from the onset of hypothermia until rewarming had raised the body temperature to approximately 30°C., occupied approximately five hours. Platelet counts were carried out by the method of Brecher and Cronkite (3) using phase microscopy. Two pipettes were filled and two chambers for each pipette were counted and the average was taken as the result for each determination. By this technique, the normal range for platelet counts in dogs is 200,000 to 350,000 per cu. mm. Leukocyte counts were carried out by the standard hemocytometer technique using 1: 20 dilution. Both sides of two hemocytometer chambers were counted. Hemoglobin concentration was measured by the cyanmethemoglobin method (4). Hematocrit was measured in capillary tubes after high-speed centrifugation (5).Protocol 1: Bone marrow aspirations and biopsies were carried out from the ribs and tibias of three dogs before, during, and after hypothermia.Protocol 2: Studies with radioactive platelets were carried out in dogs using a donor (Dog A) and a recipient (Dog B). Two mc. of Pa (NaHP"0O, Abbott) was injected into Dog A. One week later, Dog A was bled by cardiac puncture, and 500 ml. of blood was drawn into a plastic bag containing disodium versinate solution. Simultaneously 500 ml. of blood was taken from Dog B. Dog B was then transfused immediately with the blood from Dog A containing radioactive platelets. Onehalf hour later, using siliconized equipment and a two syringe technique, 15 ml. of blood was taken from Dog B. Platelets and plasma were separated from red cells by differential centrifugation and the platelets were counted in a hemocytometer chamber using a phasecontrast microscope. The platelet suspension was then centrifuged to throw down the platelets. The platelets were washed ...

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This paper summarizes the evidence in favor of the theory that many of the platelet’s factors are adsorbed onto its surface from the plasma. It is suggested that this ability of the platelet is one of its basic functions. The platelet adsorbs coagulation and perhaps vascular factors on its surface and carries them through the circulation to the area where they are needed most—at the site of vessel wall injury. This adsorption by the platelet may be an active rather than a passive process, since it requires the expenditure of energy and since it continues only so long as the platelet is viable. In those diseases in which there is marked abnormality of the plasma proteins, there is evidence to suggest that associated coagulation and hemostatic defects may be due to interference with this "atmosphère plasmatique."