OPSONINS 211 



tive capsules. Some show other alterations which evidently have the 

 same purpose. We distinguish between "animal" and "culture" bac- 

 teria inasmuch as the former are more resistant especially to the 

 destructive secretions of the body cells. 



Observation shows that most of the bacteria taken into the leuko- 

 cytes are completely digested. The bacterial cells become pale, then 

 granular, and finally disappear altogether. Occasionally a phagocyte 

 takes in more bacteria than it can digest and injures itself, in some 

 cases, fatally. The digestive phenomena are identical in the test-tube 

 and in the body. The tubercle bacillus, although readily engulfed by 

 phagocytes, is not digested. These bacilli probably owe their protec- 

 tion to the abundant deposits of wax and fat which they contain. The 

 intracellular ferment of the phagocytes is studied by collecting a large 

 number of leukocytes and dissolving them in very dilute acid or alkali 

 or breaking them down by alternating freezing and thawing. . This 

 ferment is not destroyed by a temperature of 65 C. It is able to 

 digest many bacteria, such as streptococci and pneumococci, which are 

 not affected by extracellular ferments. Levaditi found that the intra- 

 cellular ferment of the polynuclear cells acts on bacteria but is with- 

 out effect on red corpuscles, trypanosomes and spirochetes, while that 

 of the large mononuclear cells acts on the latter group and has but 

 little or no action on bacteria. Opie found the ferment from the poly- 

 nuclear cells, which he calls leukoprotease, acts in neutral or feebly 

 alkaline solution, while that from the large mononuclear cells, which 

 he calls lymphoprotease, acts only in acid solution. When leukopro- 

 tease is set free in the body by the disruption of the polynuclear leuko- 

 cytes, its action is inhibited by soluble substances in the plasma. When 

 lymphoprotease is set free in the blood, its action is inhibited by the 

 alkalinity of the fluid. It appears from this that, physiologically, both 

 of these ferments are active only within the cells which elaborate them. 

 It is by virtue of these intracellular ferments that the phagocytes kill 

 and digest the bacterial and other cells which they engulf. 



Whether the action of opsonins on bacteria is wholly physical, 

 wholly chemical, or both, we do not know. Neufeld states that this 

 action is not chemotaxic, because unsensitized bacteria, in suspension 

 with phagocytes, collect about the latter quite as plainly as sensitized 

 bacteria do; but with the former there is no phagocytosis. It seems 



