122 METHODS OF EXAMINING SERUM 



The emulsion, corpuscles, and serum being thus prepared, an 

 equal quantity of each is taken by a small capillary pipette, and 

 a thorough mixture is made in the usual way. A small portion 

 of the mixture is taken up in a capillary tube, and its ends are 

 sealed by heat, care being taken that the contents are not over- 

 heated. The tube is then placed in the incubator at 37° for 

 fifteen minutes. At the end of this time a drop of the mixture 

 is placed_on a slide, and a film preparation is made, this in the case 

 of ordinary bacteria being stained by Irishman's method. With 

 tubercle bacilli the following is the procedure : The film is fixed, 

 washed thoroughly, stained with carbol-fuchsin as usual, de- 

 colorised with 2 - 5 per cent, sulphuric acid, cleared with 4 per 

 cent, acetic acid, washed with water and counter-stained with 

 watery solution of methylene-blue (to which \ per cent, sodium 

 carbonate may be added), and dried. 



The two preparations are now examined microscopically with 

 a movable stage, the number of bacteria in the protoplasm of at 

 least a hundred polymorphonuclear leucocytes is counted, and 

 an average per leucocyte struck; the proportion which this 

 average in the case of the abnormal serum bears to the average 

 in the preparation in which the healthy serum was used, con- 

 stitutes the opsonic index — that of healthy serum being reckoned 

 as unity. 



In the case of such organisms as those of the coli-typhoid 

 group and cholera, which are susceptible to bacteriolytic in- 

 fluences in the serum, it may be necessary to heat the sera of the 

 patient and observer for half an hour at 55° C. This destroys 

 any complement present and prevents bacteriolysis occurring. 

 In the case of the b. typhosus the virulence of the strain em- 

 ployed has been shown to be an important factor. 



Several modifications of Wright's technique have been sug- 

 gested. For example, Simon compares not the numbers of bacteria 

 ingested, but the percentages of cells containing bacteria and 

 those not containing bacteria. This he calls the " percentage 

 index," and he states that the figure thus obtained corresponds 

 very closely to the ordinary opsonic index ; he claims that the 

 method eliminates some of the errors which may arise in the use 

 of the ordinary technique if only a relatively small number of 

 phagocyting cells, such as 50, be examined. 



Bactericidal Methods — -Deviation op Complement. 



The Estimation of the Bactericidal Action of Serum. — This 

 may be carried out by various methods, of which those of 



