I90 MILK AND THE PUBLIC HEALTH 



after 2 days' incubation at 37 0. for tfie characteriHtic changes 

 described on page i'2. In the slender test tubes advocated 



the '2 c.c. of milk rather more 

 than half fills the tube, and the 

 condition of the milk can readily 

 be observed. The tubes lieing 

 small readily go into a small 

 s[>ecimen jarwliicli consequently 

 requires less chemicals to ab- 

 sorb all the oxygen, while space 

 in the incubator is economised. 

 The essential value of th(_' motli- 

 hcation is that tlie test is made 

 much more delicate witlwut ad- 

 ditional work. 



Some arbitrary standard is 

 convenient for recording. Each 

 [)0siti\'e result in a tube is 

 counted as 1 B. cnierituli^ s/iiirii- 

 (ji-nrs spore, .-in assumption whicli 

 is probably, but certairdy ncit 

 always, true. Thus, if all the 

 ten tuljes show a positive " enteritidis change," the result is 

 recorded as 10. W\ graxlations between and 10 may lie met 

 wdth, and a comparative sensitive test is in this way available. 

 It is not usual to confirm the diagnosis liy an animal 

 inoculation test, reliance being placed upon the naked-eye 

 changes in the test tube, the so-called " enteritidis change." 

 From the facts given in Chapter IV. it is evident that other 

 organisms, such as B. luitijrltrus, give this appearance in Uiilk. 

 Since, however, these other organisms have, as far as is known, 

 a very similar distribution in nature this fact does not in- 

 validate to any serious extent the value <jf tlie test. If 

 pathogenicity is to lie tested 1 c.c. of the whey is injected 

 subcutaneously into a guinea-pig. 



One great value of tins test is that it is a non-midtijilyint;- 

 one, so that it is especially useful for vended milk. A 

 drawback to its utility is the fact that the spores are not 

 always uniformly distrilmted in the nnlk. 



Fiu. 8. 



