564 MICRO-ORGANISMS AND DISEASE [chap. 



ophthalmia, in gonorrhoea, in tubercle, and particularly in 

 the leprosy cells of the leprous tubercles. The presence of 

 the microbes in the interior of cells in these cases means 

 just the reverse of a destruction of the microbes by the cells, 

 it means a destruction of the cells by the microbes, the 

 latter multiplying in the former and thereby producing their 

 (the cells') ultimate destruction. 



The occasional local leucocytosis observed in connection 

 with immunity, i.e. occurring at the seat of introduction of 

 bacteria, is explained by a remarkable attraction which the 

 introduced microbes seem to exert on the leucocytes. 



Pfeffer made the first observations as to the remarkable 

 power possessed by different chemical substances towards 

 bacteria and other micro-organisms, substances which either 

 attract or repel bacteria, these phenomena being spoken of 

 as chemiotaxis, the former as positive, the latter as negative 

 chemiotaxis. Pfeffer (Unters. a. d. bot. Inst. Tubingen., 

 1887, p. 582) found that motile organisms (bacteria, flagel- 

 lata, and volvocinea) are stimulated by many organic and 

 inorganic substances in solution — positive chemiotaxis. To 

 mention only a few of the substances, the salts of potas- 

 sium have a great " stimulating " power, likewise peptone, 

 glycerine, morphine. Alcohol, free acids, and free alkalies 

 have a negative chemiotactic action, /.a'., repel the microbes. 

 Ali Cohen (Centr. f. Bakt. und Farasit., viii. 6) made 

 systematic observations on this same subject vi'ith various 

 kinds of bacteria. 



Gabritschevsky, Massart and Bordet {Annaks de V Instiiut 

 Pasteur, 1891, iv. 6), and others tested then the action of 

 bacteria on leucocytes, introducing chemical substances in 

 capillary glass tubes into the living body of animals, and 

 then examining these capillary tubes and seeing whether 

 they attracted leucocytes or not ; in this way they found 



