A QUANTITATIVE increase in platelet adhesiveness after operation was first demonstrated by Wright in 1942. This finding has been confirmed by Moolten, Vroman, and Vroman (1949). In addition, Emmons and Mitchell (1965) have shown changes in plateletclumping activity in response to adenosine diphosphate (ADP), adenosine triphosphate (ATP), and noradrenaline after operation. However, in these reports the patients have had operations of varying severity and such variables as the preoperative state of the patient, operative blood-loss, intravenous infusions, and postoperative complications have not been specifically excluded. It is possible that the changes demonstrated may have been related, at least in part, to these factors. We therefore decided to study a series of patients in whom complicating factors, which might affect the platelet adhesiveness, were excluded as far as possible. In addition, a number of measurements have been made during the first 2 days after operation since, in the reports referred to above, this period was not studied in detail.
We have also obtained information on the changes in total platelet counts in the same group of patients. These changes are important in considering the mechanism of the changes in platelet adhesiveness.
MATERIAL AND MJZTHODS
Twenty-six male patients aged between 20 and 75 years (mean 47.8 years) were studied. None had associated diseases with the exception of 2 who had evidence of ischaemic heart disease. Their bodyweights ranged from 63 to 91 kg. (mean 71.8 kg., S.D.f10.7 kg.); all were on a normal diet prior to admission and none had lost weight. Haemoglobin estimations were performed in all subjects, the range being from 13.0 to 15.5 g. per 100 ml. (mean 14'3 g., S.D. fo.6 g.).
The operations performed were :- Herniorrhaphy I8 Partial excision of hydrocoele 2 Laying open of fistula in ano 2 Laying open of pilonidal sinus 2 Excision of multiple lipomata 2
Anaesthesia was with thiopentone, nitrous oxide, and halothane in 22 patients; the remaining 4 had thiopentone and nitrous oxide, with 2 of these having a relaxant drug as well.
In the first 12 patients (Group I) blood samples were taken before operation, and at 4, 4, 24, and 48 hours after its completion. In 14 patients (Group 2) samples were taken before, and on the second and sixth days after operation. With the exception of those at 3 and 4 hours postoperatively, all samples were collected between 8.15 and 8.45 a.m. The