DEPARTMENT OF EMBRYOLOGY. 117 



physical system characterized above all by its response to finely particu- 

 late matter. In the case of particles of ordinary microscopic dimen- 

 sions, this response (phagocytosis) is a behavior shared equally with 

 the polymorphonuclear elements of the blood. But towards the very 

 much finer ultramicroscopic particles the macrophages react in a prac- 

 tically specific way, '' drinking them in," as it were, and storing them 

 either as free coagula in their protoplasm or as the inhabitants of watery 

 vacuoles, where they oscillate in ceaseless Brownian movement. 



From his definition of the macrophages he proceeds to a consid- 

 eration of their function in the body. He regards them as storing 

 substances of importance to the organism which are in the colloidal 

 state. There is little doubt that tliis action in this capacity obeys the 

 principle of a physiological balance, for only in cases in which the local 

 or general content in the substance is very high do they load with it, 

 and they no doubt liberate their content to an impoverished fluid. 

 For the latter phenomenon an analogy is found in the occurrence of 

 decolorization of animals stained by these dyes, where the liberation of 

 their dye content by the m.acrophages stands in direct relation again with 

 the physical character of the dye solution, highly dispersed ones escaping 

 rapidly, highly colloidal ones adhering stubbornly to their depots. 



In all of these processes connected with tissue destruction the macro- 

 phages house the complex chemical bodies set free, and thus become the 

 great cells finally so apparent to the eye. There is a growing recog- 

 nition of the fact that many of these bodies are in colloidal systems like 

 the dyes. 



Another contribution to the knowledge of macrophages is furnished 

 by Dr. C. R. Essick's work on the transitory cavities of the corpus 

 striatum of the human embryo. The reference concerning the exact 

 morphology of the cavities is given elsewhere. Essick found in these 

 cavities a great number of peculiar cells which exist also in other parts 

 of the embryo and v/hich show the following characters: they are 

 very large, much larger than the erythrocytes; they often build 

 pseudopodes; their protoplasm is finely granular and vacuolar; their 

 most important character is the presence of inclusions, especially of 

 erythrocytes, which can be found in the different phases of intracellular 

 digestion. This last feature shows that these cells really belong to the 

 class of macrophages; they are extravascular phagocytes. 



Miss K. J. Scott's researches on vitally stained cells of the subcu- 

 taneous tissue of the mouse lead her to the conclusion that isamine or 

 trypan blue is not associated with some preformed element of the living 

 cells, but is simply stored in the cytoplasm — as Evans and Schulemann 

 thought — by a sort of ultramicroscopic phagocytosis. In this special 

 case Miss Scott shows, contradicting Tschaschin, that the elements 

 colored in vivo in the cells of the subcutaneous tissue by the isamine blue 

 are not mitochondria. 



