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We have chosen the above title for this analysis since the following discussion is an extension of an article by W. O. Fenn with the same title. 1 Fenn's theoretical analysis of the behavior of a hypothetical fluid cell in contact with a flat solid surface was an attempt to solve the problem without using the mathematical fiction of a "surface tension." From consideration of the free surface energy of the cell, he showed that conditions of equilibrium between a cell settling and spreading on a plane surface can be predicted, completely, in terms of the contact angle between cell and surface. Using the same method of attack he endeavored to show that in general, when a cell spreads over a solid particle (ingestion of the particle by the cell) all equilibrium conditions could be predicted from a knowledge of the magnitude of the contact angle alone. Unfortunately, "even with the expert assistance of a professional mathematician" he was not able to arrive at a general solution so that he limited himself to a special case, in which the cell's diameter was four times the magnitude of the particle's diameter, and discussed this in detail. He concluded that the particle cannot be completely ingested unless the surface tensions at the interfaces are such that the cell in the same environment can spread to infinity when placed on a flat surface of the same substance as the particle. In order to simplify the analysis of the general case, about to be considered, we have reviewed Fenn's discussion of the behavior of a perfectly fluid cell in contact with a plane surface by means of a simplified solution. Using the same notation adopted by Fenn we will assume the existence of a spherical cell C about to settle on a plane glass surface G, both completely immersed in plasma P. Distortions in the cell due to the gravitational field are here considered negligible. We wish, as in Fenn's solution, to consider the various positions that such a cell will assume as it settles and spreads over the glass surface. Fig. 1 shows the position of the cell in the act of spreading with the conventional

THE THEORETICAL RESPONSE OF LIVING CELLS TO CONTACT WITH SOLID BODIES