182 PUBLIC HEALTH BACTERIOLOGY . 



marrow, are the chief examples. Metchnikoff calls the poly- 

 morphonuclear leucocytes, Microphages, and all the other 

 phagocytes, Macrophages. He observed the phagocytosis 

 in a fungus disease of a water-flea (Daphnia), and in frogs 

 infected with anthrax, where the death and dissolution of 

 the bacilli could be seen going on inside the phagocytes. 

 Later researches proved that the same phenomena could 

 be observed in all infective processes, more especially if 

 the animal were resistant to the infection. When the 

 micro-organisms get into a part where few phagocytes 

 are, a migration towards the affected spot occurs. This 

 is part of the inflammatory reaction which follows infection. 

 The cause of this migration is the presence of substances 

 in the part, which attract the phagocytes, and is known 

 as positive chemiotaxis. Negative chemiotaxis, or the 

 repulsion of the phagocytes, also occurs. Buchner showed 

 that dead bacteria, bacterial proteins, and closely allied 

 substances, such as vegetable casein (legumin), have a 

 positive Chemiotaxis, whilst the toxins of many virulent 

 bacteria have a negative chemiotactic power. In natural 

 immunity, phagocytosis is developed to a high degree, 

 and it is of such constant and regular occurrence that 

 we may often foretell from the degree of phagocytosis 

 whether, in a particular infection, the animal being 

 experimented with will gain the victory or not. A clinical 

 application of these results is seen in the observation of 

 the increase of the number of leucocytes in the blood 

 during the progress of a disease like pneumonia. The 

 increase is called " Leucocytosis," and is almost wholly 

 of the polymorphonuclear variety. In pneumonia an early 

 and marked leucocytosis is a sign of favourable import, 

 and may be from 12,000 to 40,000 per c.mm. The absence 

 of leucocytosis, except in very slight infections, is highly 

 unfavourable. (It is interesting to note here that whoop- 

 ing-cough gives a Lymphocytosis, as also do enlarged 

 tonsils, rickets, scurvy, and a few other diseases.) 



2. The Action of the Blood Serum. Besides the 

 direct action of the phagocytes, as described by Metchnikoff 

 (the cellular theory), the blood seium was found to have 

 bactericidal power. Von Fodor showed that freshly 

 drawn rabbit's blood could destroy anthrax bacilli, as 



