1. A modified falling ball viscometer (rolling ball viscometer) for blood and other humors is presented. It is capable of easily measuring flow properties at several stresses, as is required to define satisfactorily the properties of anomalous flow systems. At high shearing stresses, apparent specific viscosity values of 2.5 + are observed, corresponding to 2.2 ±0.2 reported as possible with the biological viscometer of Whittaker and Winton.

2. Previous references to the anomalous flow properties of blood were verified. It was demonstrated that these systems conform to the Bingham concept of anomalous flow. To define completely the flow properties of such systems it is necessary to make determinations at at least two shearing stresses, preferably more. Data are reported for the pseudoviscosity and yield value, the latter being possibly the most specific property of the three bloods studied.

3. Heparin in increasing amounts tended to decrease the apparent viscosity, pseudoviscosity, and yield value of blood. Similar increases of heparin also reduced the viscosites of the serum and plasma.

4. The ratio of the apparent viscosity of blood and its plasma was found to be reasonably constant as reported by Trevan. However, as the apparent viscosity is a function of the shearing stress, it is believed that the relationship for the calculations of corpuscular concentrations, such as the Whittaker and Winton modification of the Hatschek formula, is specific for the instrument and conditions of tests by which it was determined.

5. Heparinized blood was found to exhibit thixotropy, dilatancy, and age-hardening phenomena.

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