876 PHAGOCYTES AND PHAGOCYTOSIS IN IMMUNITY 



tion of leukoprotease. In the later stages the exudate is composed chiefly of mono- 

 cytes and is acid in reaction. Experiments show that the enzyme of these cells works 

 best in an acid reaction (0.2 per cent acetic acid) but is inactive in a neutral or alkaline 

 reaction. This enzyme is more thermolabile than leukoprotease, being injured at 60°- 

 70° C. It closely resembles the autolytic enzymes of parenchymatous tissues. 



Ferments resembling these two have been described by Lord/ Lord and Nye/ 

 and Nye^ from the pneumonic lung. One digests coagulated blood serum at pH. 7.3- 

 6.7; and the other splits peptone to the amino acid stage at pH 8.0-4.8 (most active 

 at pH 6.3-5.2). 



Jobling and Strause^ found in fresh pus cells an erepsin-like ferment capable of 

 splitting peptone. 



Thus to summarize and give a brief picture of the present conception of phago- 

 cytosis: During the acute stage of inflammation the polymorphonuclear cells invest, 

 take up, and attempt to digest the foreign body. In many instances, opsonin — when 

 present in sufficient concentration — greatly facilitates ingestion. If the foreign body 

 be of the nature of a living micro-organism it is presumably first opsonized and then 

 taken up, and digested or not as the case may be. The action of the leukoprotease of 

 the polymorphonuclear cells is usually limited to substances within the cell, for any 

 ferment which is secreted or shed as the result of injury is promptly neutralized by 

 the non-specific anti-ferments of the blood. However, the destruction of the leuko- 

 cytes often becomes excessive or the local edema dilutes the anti-ferments and more 

 leukoprotease being freed than can be neutralized there is solution of the fixed-tissue 

 cells. In those infections in which the polymorphonuclear cells play a dominant role, 

 if the elimination of the infecting agent has been successful, the process becomes 

 chronic and is followed by repair. During these later stages the monocytes play a 

 dominant role. It is probable that these cells are mainly derived from pre-existing 

 free phagocytes. That they can multiply has been proved by their cultivation in vitro 

 by Carrell and Ebeling.s Or, also, they may be derived by the multiplication of the 

 endothelial cells of pre-existing capillaries or from newly formed capillary sprouts.*" 

 Lewis and Lewis^ have seen leukocytes in cultures become transformed into cells 

 identical with clasmatocytes, epithelioid cells, and multinuclear giant cells. They sug- 

 gest that such transformation may occur in the body wherever the circulation is slug- 

 gish, e.g., sinuses of spleen and tissue spaces. 



These monocytes are engaged chiefly in the removal of foreign material which is 

 absorbed with difficulty, such as nuclear material, blood corpuscles, and the blood pig- 

 ments hemosiderin and hemofuscin, malarial pigment, etc. In some parasitic diseases 

 the endothelial cells are stimulated to overgrowth as in tuberculosis, leprosy. Rocky 

 Mountain spotted fever, typhus, typhoid, measles, Leishmaniasis, amebiasis, malaria, 

 etc., and the defense of the hosts seems to be largely dependent on the phagocytic 



' Lord, F. T.: Jour. Exper. Med., 30, 379. 1919. 



2 Lord, F. T., and Nye, R. N.: ibid., 34, 199. 1921. 



3 Nye, R. N.: ibid., 35, 153. 1922. ^ See Opie: Physiol. Rev., 2, 552. 1922. 

 s Carrell, A., and Ebeling, A. H.: J. Exper. Med., 36, 365. 1922. 



^ Foot, N. C: ibid., 34, 635. 1921. 



7 Lewis, M. R., and W. H.: J.A.M.A., 84, 798. 1925; Am. J. Path., i, 91. 1925. 



