IT IS WELL known that drawn blood does not possess the same properties as circulating blood. With the knowledge that blood usually undergoes certain changes as soon as it comes into contact with any material that is not normally a part of the vascular tree, it would appear natural to make observations concerning its physiologic reactions while it is passing unmolested through the vascular bed. To achieve this end not only must one maintain the physiologic state of the tissues in question but microscopic examination requires illumination and the source of light must not be a source of heat or the observations become invalid.
Since the discovery of circulation in 1629 by William Harvey, it is interesting to note how little attention has been paid to the microscopic study of circulation in the living tissues. Special technics and careful manipulation of tissues are required. Methods used in this study are