CHAPTER LXV 

 THE MECHANISM OF PHAGOCYTOSIS 



W. O. FENN 

 School of Medicine and Dentistry, The University of Rochester, Rochester, N.Y. 



THE ROLE OF FREE-ENERGY CHANGES IN PHAGOCYTOSIS 



From a very general point of view phagocytosis may be regarded as a problem of 

 cell permeability, there being a continuous and gradual transition from molecules 

 through colloidal particles and fine suspensions to particles nearly as large as the 

 phagocyte. In cases where penetration of molecules involves an approach to a true 

 equilibrium, i.e., a diminution of free energy, an accurate analysis of the factors in- 

 volved is much facilitated. The question arises, therefore, whether phagocytosis is 

 such a process, or whether the ingestion of particles involves an increased metabolism 

 on the part of the cell, some of this extra energy being stored up as potential energy 

 of position or as surface energy between the cell and the particle. At the outset of an 

 inquiry into the mechanism of phagocytosis it must be admitted that to this most 

 fundamental of all the questions involved we have no unequivocal answer ready. // 

 is not certain whether phagocytes ingest objects because of surface tension or in spite of it. 

 Probably there is truth in both. 



There are cases, however, in which it appears certain that the diminution of free 

 energy resulting from ingestion is a limiting factor in the process. Thus in a mixture 

 of polymorphonuclear leukocytes of the rat with equal-sized particles of carbon and 

 quartz, a certain microscopic field was examined' showing 77 leukocytes, 44 carbon 

 particles, and 38 quartz particles. After twenty-four minutes, 36 chance contacts 

 had been observed between leukocytes and quartz particles and 37 contacts between 

 leukocytes and carbon particles. Yet at the end of this period only i quartz particle 

 was to be seen inside a leukocyte as compared with 12 carbon particles. In this case, 

 then, the chances of collision for the carbon and quartz particles were equal but the 

 chance of penetration favored the carbon 12 to i. Between these two insoluble 

 particles the leukocyte is evidently able to detect a difference. This cannot be due, of 

 course, to a chemical difference in the medium, caused, for example, by materials 

 which leach out of the pores in the carbon, for both kinds of particles are incubated 

 together under the same cover slip. It is difficult, therefore, to believe that the differ- 

 ence can be anything but a diflference in the surface-energy relationships. 



This observation alone, however, does not prove this to be a fact. Amebae have 

 been observed to cut Paramecium in two parts in the process of ingesting it.^ Surface 

 energy relationships could have made very little difference to this ameba, which was 

 reacting as a whole to some stimulus. A high surface energy between the Paramecium 



' Fenn, W. O.: /. General Physiol., 5, 311, 1923; 3, 575. 1921. 

 'Mast, S. O.: /. Morph. b' Physiol., 41, 347. 1926. 



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