94 



MILK 



temperature for ten minutes, then cooled and incubated ana- 

 erobically as described in Chapter II. 



The amounts given above are too wide apart to yield a 

 satisfactory estimation, and the following method is advocated 



by the writer 1 : quite small, nar- 

 row (4 by J inch), sterile empty 

 test tubes are used in batches of 

 ten for each estimation, 20 c.c. 

 of milk is employed for each 

 test, 2 c.c. being added by sterile 

 pipette to each tube. The ten 

 tubes are heated for 10 minutes 

 at 80 C, rapidly cooled and in- 

 cubated anaerobically in speci- 

 men jars with ground -glass 

 stoppers, just large enough to 

 take the ten tubes (Fig. 10), 

 the oxygen being absorbed by 

 the usual potash and pyrogallic 

 acid mixture. The tubes are 

 examined after two days' incuba- 

 tion at 37 C. for the characteristic 

 changes described in Chapter I. 

 In the slender test tubes advo- 

 cated the 2 c.c. of milk half fills the tube, and the condition of 

 the milk can readily be observed. The tubes being small 

 readily go into a small specimen jar which consequently requires 

 less chemicals to absorb all the oxygen, while space in the incu- 

 bator is economised. The essential value of the modification 

 is that the test is made much more delicate without additional 

 work. 



Some arbitrary standard is convenient for recording. Each 

 positive result in a tube is counted as one B. enteritidis spore, an 

 assumption which is probably, but certainly not always, true. 

 Thus, if all the ten tubes show a positive " enteritidis change," 

 the result is recorded as 10. All gradations between o and 10 



Fig. 10. 



1 Local Govt. Board Medical Officer's Report) 1909-10, p. 477. 



