IMMUNITY 199 



recovered from an infection or which has been treated in 

 the laboratory, other ferments develop which did not exist, 

 or hardly existed, before the appearance of immunity : these 

 are the sensibilisatrices, or immune-bodies or amboceptors 

 of Ehrlich. They are secreted by the macrophages to some 

 extent, but chiefly by the microphages, and are found in the 

 spleen, in the lymphatic gland, and the bone marrrow at 

 a stage in the immunizing process when they are still 

 absent from the blood. They resist a higher temperature than 

 the complement, and have properties resembling the ferment 

 enterokinase of the small intestine. Just as the enterokinase 

 prepares fibrin for the action of trypsin, so the immune-bodies 

 prepare the bacteria or other cell-elements for the action of the 

 complement : this is an analogy between extracellular and 

 intracellular digestion which ought to be emphasized. 



There is not in any given animal a series of different com- 

 plements : the complement from the same animal performs 

 indifferently haemolysis and bacteriolysis, and dissolves equally 

 well the typhoid bacillus and the cholera vibrio. The immune- 

 bodies, on the contrary, are specific, being developed during the 

 immunization against the invading cells (by inoculation or 

 natural infection). 



Complement is discharged into the fluids bathing the phago- 

 cytes only when phagolysis has occurred : the immune-bodies, 

 on the other hand, are readily excreted by the phagocytes ; they 

 resemble, not zymase, which is firmly bound to the protoplasm 

 of the yeast cell, but sucrase, which is easily discharged. 

 Recovery or inoculation does not increase the quantity of com- 

 plement, but greatly develops the quantity of immune-body. 

 In natural immunity the presence of immune-body is difficult 

 to demonstrate, probably because there is little of it in existence, 

 and what there is is contained in the phagocytes ; but in 

 acquired immunity immune-body is abundant and is found, not 

 only in the plasma and serum of the blood, but in exudates and 

 oedematous fluids. Examples of acquired immunity exist in 

 which the body remains poor in immune-body and in which 

 the body-fluids entirely lack it ; in these it is necessary to 



