RESULTS OF PHAGOCYTOSIS 185 



of digestion. The ameba, for example, is able to kill and digest en- 

 gulfed material through an intracellular ferment regarded as a form of 

 trypsin, demonstrated by Mouton 1 and called amebadiastase. Ac- 

 cording to Metchnikoff, the digestion of erythrocytes and tissue frag- 

 ments is accomplished through an enzyme of the macrophages called 

 macrocytase; that of bacteria or other substances engulfed by micro- 

 phages by a similar enzyme called microcytase. 



Following the general law that living protoplasm cannot be digested, 

 we are confronted with the very important question as to whether living 

 bacteria are engulfed by phagocytes or whether they are first destroyed 

 by extracellular agencies before they undergo phagocytosis. 



Endolysins. It seems positively established at the present time 

 that leukocytes do take up living bacteria, which may either grow in- 

 side the leukocyte or be destroyed by intracellular substances called 

 endolysins. On the other hand, leukocytes do not take up extremely 

 virulent bacteria, hence the question arises as to the importance of 

 substances in the body-fluids which neutralize the repelling substances 

 of bacteria and facilitate phagocytosis. This subject, which has con- 

 siderably modified Metchnikoff's views of phagocytosis, will be con- 

 sidered in a succeeding chapter. It will suffice here to state that leuko- 

 cytes may engulf living bacteria possessing some virulence, for not 

 infrequently an infection may be spread by bacteria transported into 

 deeper tissues by phagocytes, when they resist the germicidal activity 

 of the endolysins, bring about the death of the phagocyte, and are thus 

 liberated into new tissues. 



Death of the engulfed bacteria is, therefore, brought about by en- 

 dolysins 2 that are probably different from the digestive enzymes. These 

 substances are strongly bactericidal, and have a complex structure re- 

 sembling bacteriolysins. According to Weil, 3 they are not specific. 

 They are resistant to 65 C. or even higher, do not readily pass through 

 porcelain filters, are precipitated by saturation with ammonium sul- 

 phate, and resemble the enzymes in many respects (Manwaring 4 ). It 

 is probable that the endolysins act not only upon bacteria that have 

 been phagocytosed, but also upon free bacteria when liberated through 

 disintegration of the leukocytes. In this manner the endolysins would 

 closely resemble the normal opsonins or bacteriolysins, and support the 

 contention of Metchnikoff that these important substances contained 



1 Compt. rend, de FAcad. Sci. de Paris, 1901, cxxxiii, 244. 



2 For general review, see Kling: Zeit. Immunitate, 1910, 7, 1. 



3 Arch. f. Hyg., 1911, 74, 289. Jour. Exper. Med., 1912, 16, 250 



