96 CLINICAL BACTERIOLOGY AND H^MATOLOGY 



terms of standard agglutination units. A standard agglutination unit 

 is defined as that amount of agglutinating serum which, when made 

 up to i c.c. with normal saline and mixed with 1-5 c.c. of standard 

 culture, causes standard agglutination under the conditions of time 

 and temperature already described. In order to determine the number 

 of units any patient's serum contains, it is only necessary to divide 

 the dilution at which standard agglutination occurs by the factor 

 (marked on each bottle), which expresses the agglutinability of the 

 culture. Thus, if a serum agglutinated at i in 1,000, and the factor 

 on the label was 2-5, then the number of standard agglutinin units 

 in this serum would be- 1 !-^- or 400. Another standard culture might 

 give agglutination at i in 1,200, but in this case the factor on the 

 bottle would be 3, and the number of agglutinin units would be J-Hf-^ 

 or 400 again. In this way comparable results can be obtained with 

 standard cultures of differing sensitiveness. If there is no agglutina- 

 tion in one dilution and " standard plus " in the next lower, standard 

 agglutination is considered as occurring in a dilution f of the difference 

 above the lower tube. Thus, if there is standard plus in i in 25, and 

 no agglutination in i in 50, standard agglutination is recorded as 

 occurring at i in 35. 



The results in uninoculated persons are similar to those obtained 

 by the ordinary methods, i in 50 being regarded as diagnostic. In 

 inoculated persons two or three estimations must be made at intervals 

 of a few days. In all cases there is a rise in the strength of the 

 serum to a maximum, usually, in the case of typhoid, about the nine- 

 teenth day, followed by a fall, so that a steady rise or fall in the power 

 of the serum to agglutinate a particular organism is diagnostic. If 

 he is suffering from paratyphoid infection this characteristic curve is 

 frequently accompanied by a temporary disturbance (a slight or 

 marked rise, followed by a fall to the normal level) in the power of 

 the serum, as tested against the typhoid bacillus. 



ISOLATION OF THE TYPHOID-DYSENTERY GROUP FROM FAECES, ETC. 



(1) Prepare a thick emulsion of the faeces by shaking a mass about 

 the size of a pea with half a test-tubeful of sterile water. (It is best to 

 use an equivalent amount of the loose motion obtained after the 

 administration of an aperient.) Allow to settle for a quarter of an 

 hour or so, so that all solid masses are got rid of. 



(2) Prepare a solution of brilliant green by adding -^ c.c. of a i per 

 cent, solution of the dye to 200 c.c. of peptone-water, containing i per 

 cent, of peptone and 0-5 per cent, of salt (or add \ c.c. of a i in 10,000 

 solution to a 10 c.c. peptone-water-tube). The stain dissolves slowly, 

 and should be allowed to stand, with occasional shaking, for a couple 

 of days before use. It will keep for about a fortnight. 



(3) Inoculate a tube of this solution with three or four large loopfuls 

 of the emulsion. In the case of urine, add about i or 2 c.c. Incubate 

 over-night. 



