ON SEDIMENTATION AND ROULEAUX FORMATION—II

Abstract

From this short study of rouleaux formation several points have emerged.The first condition for rouleaux formation, and one which is fulfilled under all but unique circumstances, is that there shall be collisions among the cells. The frequency of these collisions plainly depends on such factors as the movements in the fluid, the number of cells present per unit volume, the viscosity of the fluid, and the size of the cells. The second condition is that the collisions shall result in permanent cohesions. Such cohesions will not occur if the surfaces of the cells are not sticky, if the repulsive forces between the cells are very great, or if the cells collide with one another so that the surfaces which come into contact are small. If, on the other hand, the collisions bring large surfaces into contact, permanent cohesions are likely to occur, for not only are there large surfaces over which the cohesive forces between the cells can act, but separation of these surfaces entails a considerable amount of work.The consideration of these points indicates why cells collect in rouleaux, and not in aggregates of roughly spherical form, for all contacts except those which occur at the ends of the shorter rouleaux are not permanent, whereas all contacts in which the cells are broadside on result in lasting cohesions. To this must be added the fact that discoid cells moved by a fluid orient themselves broadside on, and therefore collisions in this position are encouraged.From the mass of work on the potential difference between the red cells and the suspending fluid, it appears that, if the potential difference be reduced below a certain point, agglutination of the cells occurs, all contacts being permanent, in whatever position they occur. From this may be drawn the deduction that the repulsive forces accompanying this potential difference are sufficient to prevent the permanence of all contacts except those which involve a large extent of surface in connection with which considerable surface and cohesive forces are called into play. Before this explanation is regarded as the correct one, however, it must be shown that those electrolytes, and other substances which reduce the potential difference, do not also increase the stickiness of the cell surfaces. The cases of CaCl2 and MgCl2, which reduce the potential difference and yet do not cause agglutination, and the instance of heated plasma, which increases rouleaux formation without decreasing the potential difference, show how necessary it is to take account of this latter possibility, the importance of which has been clearly recognised by such investigators as Oliver and Barnard and Northrop.As regards the kinetics of rouleaux formation, we have found that a simple equation containing one easily evaluated constant is sufficient to describe the course of the phenomenon under such conditions as are extremely suitable for experimental purposes.This research was carried out under a grant from the Royal Society.