2l8 GENERAL BIOLOGY OF MICRO-ORGANISMS 



to emphasize the importance of phagocytosis, and the followers 

 of Buchner and Ehrlich, who fixed their attention largely upon 

 the substances dissolved in the body fluids. 



Anti-aggressins, Specific Proteolysins. Various substances 

 produced in the body as a result of infection show particular 

 ability to combat the effects of the soluble products of the para- 

 site to which the name aggressins has been given (see page 205). 

 Knowledge of these substances and their behavior is still some- 

 what incomplete, but they seem to be particularly concerned 

 with the parental digestion of foreign proteins, a process in which 

 cystolysis may be regarded as a beginning stage. Whereas, 

 however, cytolysis is concerned with the disintegration of formed 

 material, these substances now under consideration act particularly 

 upon proteins already in solution. In many instances the products 

 of the first stages in this parental digestion are toxic (disintegra- 

 tion of tuberculin and of egg-white), and some of the symptoms 

 of infectious disease, such as fever, have been ascribed to them. 

 In their general characters these lytic substances are wholly 

 analogous to the cytolysins and their action is due to at least two 

 components, an amboceptor and a complement. 



Source and Distribution of Antibodies. The exact source 

 of the antibodies dissolved in the body fluids is unknown. All 

 agree that they are derived from cells. Metchnikoff regards 

 the phagocytic cells as the important source; Ehrlich does not 

 specify, but it would seem, in accordance with his theory, that 

 any cell capable of being affected by the foreign substance should 

 be capable of throwing off cell receptors (antibodies) to combine 

 with it. Many investigators consider antibody formation to be 

 a common property of many kinds of cells, but more especially 

 of relatively undifferentiated cells such as those of the connective 

 tissue. 



Antibodies are present in greatest concentration in the blood 

 and lymph. They are absent or present only in small amount 

 in the serous fluids of the pleural, pericardial, peritoneal and 



