ISOLATION FROM F^CES 439 



Prepare plates of litmus lactose agar, Conradi agar, MacConkey 

 agar, or some other selective agar medium and dry in the warm 

 incubator. Divide the plate into four quadrants by drawing cross- 

 lines on the under surface of the glass and label a, b, c, and d. 

 Inoculate each quadrant with a 5-mm. loopful of the respective 

 dilution, spread, allow to dry in the warm incubator, and incubate 

 the plate inverted at 37 C. for twenty-four hours, when the 

 colonies should have developed. By the use of the four dilutions 

 discrete colonies should be obtained in one or two of the quadrants. 



Failing this technique, a loopful of the faeces may be emulsified 

 in 8-10 c.c. of sterile water, so as to yield a just opalescent sus- 

 pension, which, after standing for half to one hour to allow gross 

 particles to sediment, is used for the plating. 



2. The Method. 



The following is Ledingham and Penfold's method (Brit. Med. 

 Journ., 1915, vol. ii, p. 704) : 



Essentials. 



1. MacConkey's bile-salt-lactose-neutral-red-agar. 



2. Mannitol peptone water contained in Durham's tubes. 



3. Thoroughly tested specific agglutinating serums of high 

 potency for B. typhosus, B. paratyphosus A., B. paratyphosus B., 

 B. enteritidis Gartner, B. dysenteries Shiga, and B. dysenteries Y. 



The following dilutions of these serums are made with car- 

 bolised saline (0-5 per cent, carbolic in normal saline) and kept 

 in bulk preferably but not necessarily in the ice chest. 



1. P. G. mixture containing equal parts of Paratyphosus A 

 serum (1 in 66), Paratyphosus B. serum (1 in 66), and Gartner 

 serum (1 in 66). Concentration of each in final mixture = 1 in 

 200. 



2. P. T. mixture containing equal parts of Paratyphosus A 

 serum (1 in 66), Paratyphosus B serum (1 in 6,6), and typhoid 

 serum ( 1 in 66). Concentration of each in final mixture = 1 in 200, 



3. Y serum diluted 1. in 100, or 1 in 200.. 



4. Shiga serum diluted 1 in 100, or 1 in 200. 

 5 Paratyphosus A serum diluted 1 in 200. 



6. Paratyphosus B; serum diluted I in 200.. 



7. Typhoid serum diluted 1 in 200.. 

 . Gatrtner serum, diluted X in 200,. 



