832 IMMUNOLOGY 



the infections to be described herein and have followed in the main 

 Maximow's views with regard to the origin and potencies of the various 

 cells. We have simplified and used uniform terms wherever possible. 



The role of the various connective tissue cells in immunity is shown 

 by direct histological studies and by other experimental work. Thus 

 histological studies of defense reactions have demonstrated directly that 

 some cells remove parasites and various types of debris by phagocytosis; 

 that others wall off nonremovable objects and repair damage by filling 

 in cavities, regenerating certain tissues, and so forth; and that still others, 

 such as the eosinophils, show a definite pattern of behavior and seem 

 correlated with certain phases of immunity, although their exact function 

 is still uncertain. On the other hand, removal or impairment by splenec- 

 tomy, blockading procedures, and the like, of an appreciable portion 

 of the connective tissue cells have furnished evidence of the role of 

 phagocytes in the immunity of certain infections and of the role of the 

 macrophages in the production of antibodies. 



In the successful carrying out of these studies, certain technical diffi- 

 culties have to be recognized and overcome. To study cellular details 

 and especially to see transitional forms, migrating cells, and so forth, 

 early and closely spaced stages in an infection should be studied, fresh 

 material should be used, and this should be adequately fixed and stained 

 by a satisfactory technique. One of these techniques involves fixing in 

 Helly-Maximow's Zenker formol, preferably embedding in celloidin, 

 staining with dilute Delafield's hematoxylin, and counterstaining with 

 eosin azure II. In impairing the macrophage system, the time when 

 splenectomy and blockade are performed is important, inasmuch as 

 impairment is partially made good by the host in time. Furthermore, 

 splenectomy is more effective in impairing the macrophage system in 

 certain infections in which the spleen is especially active and in certain 

 laboratory animals having a high spleen weight-body weight ratio. Thus 

 the most conclusive results may be expected when certain blood infec- 

 tions are studied in dogs, rats, and mice splenectomized and blockaded 

 as rapidly and thoroughly as possible; whereas inconclusive or negative 

 results may be expected from inadequate blockade, splenectomy a week 

 or more before infection. In fact, if impairment is slight, the system 

 may even be stimulated to greater activity. 



A. Predominantly Fixed Connective Tissue cells. — From the strictly 



