332 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1937 



microbes, and digested them (pi. 1 1 , figs. 1-3) . He therefore gave them 

 the name of phagocytes and called the phenomenon which he had just 

 discovered phagocytosis. 



The phagocytes are endowed with motility and sensitiveness; 

 they direct themselves with certainty to the focus of the microbes. 

 Up to this time, science has not been able to solve the mystery of 

 how the phagocytes which are far from the point of introduction of the 

 microbes arc informed of their arrival. All that is known, is that the 

 phagocytes move about (they traverse 2 mm in an hour by means of 

 their amoeboid movements, according to the moving photomicro- 

 graphic readings), and they can go out from the blood capillaries 

 (diapedesis) to slide between stationary cells, in their effort to reach 

 the point of infection. 



Two categories of phagocytes are described: The smaller, or 

 microphages, and the more voluminous ones, macrophages. It is the 

 microphagcs especially that rush to the attack of invading micrboes 

 and absorb them. The macrophages intervene in the combat as the 

 rearguard of the microphages; when one of the latter succumbs without 

 having digested the absorbed microbes, the macrophage speedily 

 ingests the microphage crammed with microbian elements. 



Almost immediately after the penetration of bacteria into a living 

 organism, the microphages rush to the point of infection (pi. 12, fig. 1) 

 and commence to engulf the intruders. A true battle takes place 

 (fig. 2). The reinforcements of phagocytes continue to congregate, 

 and their number generally attains its maximum after 10 to 24 hours 

 (fig. 3). The macrophages which arise in the spleen, the lymphatic 

 organs, and even the connective tissues arrive later, after 9 to 14 hours; 

 they engulf the damaged cells and the microphages that have suc- 

 cumbed. A single macrophage is capable of alisorbing from 2 to 10 

 microphages crammed full of microbes. A polymorphonuclear leu- 

 cocyte (microphage) itself can absorb as many as 20 microbian spores. 



The attacking microbes on their part attempt resistance. Certain 

 ones, such as the tetanus bacillus, secrete a toxin that removes or 

 destroys the phagocytes; others, by their prodigious multipUcation 

 overmeasure the losses undergone; those which are armored with a 

 glutinous capsule (the pneumococcus and the tetrads, for example) 

 or waxlilce capsule {B. tuberculosis), or those which have time to form 

 spores (anthrax bacteria) resist the phagocyte aggression. They 

 produce new geuerations of microbes among the phagocytes which 

 are already enfeebled and thus infection spreads. 



The phagocytic defense is particularly active at the tonsil level, 

 because of the mucus of the digestive tube and the mucous secretions 

 of the digestive system, at the weakest points which are in contact 

 with the exterior environment. 



It should be noted that there also exist in several organs fixed ele- 

 ments (nonmotile cells) such as the KupfTer cells of the Uver and the 



