528 INFECTION AND RESISTANCE 



It has only recently become clearly apparent that the function of 

 intracellular digestion of foreign substances, such as invading bac- 

 teria, is not limited to the circulating leucocytes but is to a very 

 large extent also carried on by the fixed cells of organs. Studies 

 by Wyssakowitz, 9 by Kyes, 10 by Bartlett, 11 and, recently, by Hopkins 

 and Parker, 12 have shown that in the course of many bacterial infec- 

 tions the greater proportion of invading bacteria is taken care of 

 by cells of the liver, spleen, and especially the lung. Streptococci 

 injected into rabbits rapidly disappear from the circulation, largely 

 because they are taken up very actively by the (probably) endothelial 

 cells of the lung where apparently they are killed, their digestion 

 taking place within the cells very slowly. The endocellular enzymes 

 bringing this about can, of course, not be separately studied as can 

 those of leucocytes, for obvious technical reasons. 



While the cellular enzymes have been very carefully studied, it 

 is only of relatively recent years that much attention has been paid 

 to the enzymes present in the circulating blood. This is to some ex- 

 tent due to the fact that German writers especially have taken for 

 granted that enzymes in the blood were nothing more or less than 

 liberated leucocytic enzymes, and also because the activity of the 

 circulating enzymes has been largely masked by the existence of a 

 powerful antiferment which must needs be there for physiological 

 reasons to prevent injurious autodigestion. We have already men- 

 tioned the fact that the study of pathological conditions, such as 

 myelogenous leukemia, was the point of departure for work upon the 

 leucocytic ferments, and this, to a certain extent, was also the be- 

 ginning of the studies on serum ferments. When blood serum is 

 incubated with various substrates, it is not unlikely, as we shall see 

 in our subsequent discussion of the Abderhalden reaction, that the 

 antiferment is absorbed and thereby the proteolytic and other fer- 

 ments of the blood are liberated. There is normally an excess of 

 antiferment in the blood, and normal human serum usually does not 

 contain strong proteolytic enzyme. These two factors together there- 

 fore prevent powerful proteolysis by normal serum. There are con- 

 ditions, however, under which the enzyme contents of the blood are 

 increased. Thus, the sera of pregnant women have been shown 

 to be relatively rich in proteolytic properties, and such an increase 

 is also present during starvation, as Schultz, 13 and Heilner and 

 Poensgen 14 have shown. The same thing has been noted in cases 



9 Wyssakowitz. Zeitschr. f. Hyg., Vol. 1, p. 1. 



10 Kyes. Journal of Inf. bis., 1916, Vol. 18, p. 277. 



11 Bartlett. Journ. Mcd. Res., Nov. 5, 1916, p. 465. 



12 Hopkins and Parker. In press at present writing. 



13 Schultz. Deutsch med. Woch., No. 30, 1908; Munch, med. Wocn.. Vol. 

 60, 1913. 



14 Heilner and Poensg-en. Miinch. med. Woch., Vol. 61, 1914. 



