1 90 MILK AND THE PUBLIC HEALTH 



after 2 days' incubation at 37 C. for the characteristic changes 

 described on page 42. 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 beino- 



e> 



small readily go into a small 

 specimen jar which consequently 

 requires less chemicals to ab- 

 sorb all the oxygen, while space 

 in the incubator is economised. 

 The essential value of the modi- 

 fication is that the test is made 

 much more delicate without ad- 

 ditional work. 



Some arbitrary standard is 

 convenient for recording. Each 

 positive result in a tube is 

 counted as 1 B. enteritidis sporo- 

 yenes 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 and 10 may be met 

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

 It is not usual to confirm the diagnosis by 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. lutyricus, give this appearance in milk. 

 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 of the test. If 

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

 subcutaneously into a guinea-pig. 



One great value of this test is that it is a non-multiplying 

 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 distributed in the milk. 



FIG. 



