210 A MANUAL OF BACTERIOLOGY 



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

 nisation which promote the phagocytosis of bacteria. 



Leishman's method for estimating phagocytosis* 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 driea, fixed, stained, and examined microscopically, and the 

 number of microbes ingested by the polymorphonuclear leucocytes 

 is counted. 



Wright and Douglas 2 found that washed leucocytes 

 without serum are non-phagocytic, but become so on the 

 addition of normal serum. If, however, the serum be 

 first heated to 60-65 C. before being added to the mixture 

 of leucocytes and microbes, phagocytosis does not take 

 place ; but if the unheated serum is mixed with the bac- 

 teria, the mixture kept at 37 C. for fifteen minutes and 

 then heated to 60 C. for fifteen minutes, phagocytosis can 

 still take place, thus demonstrating that the serum acts 

 in some way on the bacteria, rendering them suitable prey 

 for the phagocytes. This thermolabile serum feast pre- 

 parer is called by Wright and Douglas " opsonin " (from 

 a Greek word meaning " to cater for "). 



They have also shown that during the process of active 

 immunisation the opsonic value of the serum is increased, 

 and they have succeeded in demonstrating this opsonic 

 immunity for a number of infections, such as the staphy- 

 lococcic, Malta fever, pneumococcic, and tuberculous. If 

 it be desired to measure the quantity of opsonins present, 



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



2 Prcc. Roy. See. Lond., 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; 

 fitudies in Immunity, 1909. 



