IMMUNOLOGY 839 



cal tests. Protective and curative tests differ only as regards the time of 

 injecting the serum and organisms. In protective tests the serum is in- 

 jected at the same time (or not more than a day before or after) the 

 organisms are injected, whereas, in curative tests the serum is injected 

 some time after the organisms have been injected and generally when 

 they can be found in some particular part of the body. The effect of the 

 latter may obviously be more variable, since the organisms already have 

 a start in the body and may be more difficult to check. 



THE CELLULAR AND HUMORAL ASPECTS OF IMMUNITY 



The reader is referred to Maximow (1927b) for a general descrip- 

 tion of the histogenesis of the inflammatory and defense reactions, to 

 Aschoff (1924), Jungeblut (1930), Gay (1931), and Jaffe (1931, and 

 1938) for a general consideration of the function of cells and, in par- 

 ticular, of macrophages; and to Linton (1929), W. H. TaUaferro (1929 

 and 1934), and W. H. Taliaferro and Mulligan (1937) for a specific 

 consideration of the role of cells in protozoan immunity. 



The way in which the cells of the connective tissue, in particular the 

 granulocytes and the cells of the lymphoid-macrophage system, are in- 

 volved in local defense can be seen during the inflammation which fol- 

 lows the introduction of foreign material into connective tissue of the 

 skin. The heterophils migrate early from the blood vessels. Their number 

 and activity depend upon the nature of the inflammatory stimulus and 

 whether it is sterile or septic. They are generally not numerous in proto- 

 zoan infections and soon disappear when the inflammatory material is 

 bacteriologically sterile. Under sepsis, however, they continue to migrate 

 from the blood vessels and to combat the invading organisms in many 

 visible ways — by active phagocytosis and digestion, by the secretion of 

 bactericidal and proteolytic ferments, and the like. They represent an 

 important first line of defense since they are the most easily mobilized 

 cells, but their functions are limited since they generally disintegrate 

 within a few days, ordinarily are recruited only from the blood stream, 

 i.e., do not multiply in situ, and cannot develop into other cells of the 

 area. 



The cells of the lymphoid-macrophage system are the most important 



