Summary
When some human platelets were aggregated in vitro by exogenous adenosine diphosphate
(ADP) or adrenaline they released their own ADP. As ADP is the final stimulator of
most aggregation, this ability to produce its own release gave a self- propagating
secondary aggregation (SA) which could be marked in certain individuals and diseased
states. In a survey of several animals, this ability to produce self- propagating
aggregation was also found in a marked form in cats (which can form systemic platelet
thrombo-emboli) and to a less extent in baboons and some dogs. This property of the
platelets of humans and cats could be an important factor in their ability to form
platelet thrombi more easily than other mammals. Thus, SA and its inhibition by drugs
may be of considerable importance in the management of thromboembolic disease and
a study of such agents carried out in these animals may be reasonably regarded as
a relevant and useful preliminary to clinical trials in man.