256 A MANUAL OF BACTERIOLOGY 



no certain proof of the existence of stimulins is forth- 

 coming, although Leishman attributed a stimulin action 

 to thermostable substances in the serum in typhoid and 

 Malta fevers. Subsequently Metchnikoff conceived the 

 serum as acting, not on the leucocytes, but on the microbe, 

 causing it to become positively chemotactic and no 

 longer to repel, but to attract, the phagocytes. Consider- 

 able support was given to this view by the work of Wright 

 and Douglas, who, by a modification of Leishman' s 

 ingenious method for quantitatively estimating phago- 

 cytosis, emphasised the importance of the serum in the 

 mechanism of phagocytosis. 



Neufeld and Rimpau also concluded that substances, 

 " bacteriotropines," are produced in the course of immu- 

 nisation which promote the phagocytosis of bacteria. 



Leishman' s method for estimating phagocytosis. 1 A thin suspen- 

 sion of some micro-organism, e.g. M. pyogenes, is mixed with an 

 equal volume of blood from the finger ; a droplet of this mixture 

 is placed on a clean slide, and covered with a cover-glass, and the 

 preparation is at once placed in a moist chamber in the incubator 

 at 37 C. for half an hour. At the end of this time it is taken out, 

 the cover-glass slipped off, and the films on slide and cover- 

 glass are dried, fixed, stained, and examined microscopically, and 

 the number of microbes ingested by the polymorphonuclear 

 leucocytes is counted. 



Wright and Douglas 2 found that leucocytes washed 

 free from serum are non-phagocytic, but become so on 

 the addition of fresh normal serum. Serum heated to 

 60 C. is inactivated and no longer induces phagocytosis. 

 If bacteria be treated with fresh serum at 37 C., washed 



1 Brit. Med. Journ., 1902, vol. i, p. 73. 



2 Proc. Roy. Soc. Land., B. Ixxii, 1903, p. 357 ; B. Ixxiii, 1904, p. 128 ; 

 B. Ixxiv, 1905.. pp. 147, 159 ; B. Ixxvii, 1907, p. 211. Also in Practitioner, 

 May, 1908 ; various papers in Lancet and Brit. Med. Journ. ; Wright, Studies 

 in Immunity, 1909. 



