CELLULAR RESISTANCE 157 



surface of the mercury drop whereby the surface tension of this side 

 is lowered, thus causing the progressive movement in the direction of 

 the dichromate crystal. Similarly a drop of clove oil in a mixture of 

 glycerol and alcohol will move about and send out pseudopodia in much 

 the same manner as an ameba. The movement depends upon the solu- 

 bility of the clove oil in alcohol, but the glycerin retards the diffusion 

 and thus determines a certain degree of irregularity in the movements. 

 If strong alcohol be introduced near the clove oil the surface tension 

 of the oil is reduced and it moves toward the alcohol. Heat applied 

 near one side of the drop will also lower the surface tension, and it 

 moves toward the point of heat positive thermotaxis. These experi- 

 ments illustrate the physical basis of ameboid movement, but do not 

 explain ingestion of particles. For this purpose a drop of chloroform 

 may be placed in water and brought near a variety of objects, such as 

 glass particles and small pieces of shellac, paraffin and glass. Such a 

 drop will flow around a piece of shellac and dissolve it. A piece of 

 glass covered with shellac will be taken up, the shellac dissolved and 

 the piece of glass then extruded. If a long " hair " of shellac is 

 brought into contact with the chloroform, the former will be bent in 

 the middle, pseudopodia will extend along it and it will finally be 

 curled up inside the drop and dissolved. These various activities of 

 the oil drop or chloroform drop resemble in detail the activities of 

 amebae under similar circumstances and may be understood as indi- 

 cating that the process of phagocytosis is based on definite physical 

 laws. The experiments do not explain all the phenomena, however, 

 and must be interpreted as solving the problem only partially. Various 

 food particles are not soluble in the cytoplasm of the ameba, bacteria 

 are not soluble in the cytoplasm of the leucocytes, but in each instance 

 must be digested in some way. Furthermore, the phagocytes have the 

 property of taking up inert and insoluble particles such as coal dust 

 and other pigments, substances which cannot exert chemotaxis nor 

 alter surface tension. The artificial ameba does not assimilate, it 

 merely dissolves. An additional differentiation between the leucocytes 

 and the ameba is the fact that the ameba is a free living organism 

 capable of nourishing itself independently of life within another or- 

 ganism. On the other hand, the leucocyte depends upon the blood for 

 its nutrition and differs in ameboid movement and irritability from 

 the free living ameba. Thus we must conclude that the problem of 

 phagocytosis is not solved by these experiments and that the life activ- 

 ities of these cells are not as yet explainable on a purely physical basis. 

 Influence of Temperature on Phagocytosis. Madsen and his 

 school have made accurate studies of the influence of temperature 

 on phagocytosis. They have shown that within certain limits the 

 phenomenon of phagocytosis increases with the degree of tem- 

 perature. Starting at a point of =*= 5 C., the phagocytic power 

 increases with temperature up to the normal temperature of the species 

 from which the phagocytic cells are derived. In cold-blooded animals, 

 on the other hand, the temperature of the environment within certain 



