1911.] Constituents of a Bacterial Emulsion, etc. 



325 



Wliy does a Suspension of Washed Bacilli such as used in the foregoing 

 Experiments fail to give Satisfactory Indications in Opsonic Power ? 

 And why does the Addition of Detritus improve it in this respect ? 

 Eeflection shows that, when we are testing a series of sera with a view to 

 eliciting differences in their bactericidal agglutinating or opsonic powers, we 

 cannot expect that the full differences will be revealed unless the bacterial 

 suspension which we employ contains more microbes than the strongest 

 blood is competent to kill, agglutinate, or opsonise. And we can be certain 

 that if the bacterial suspension contains only such number of microbes as 

 the weakest blood is able to kill, agglutinate, or opsonise, no differences can 

 be expected to emerge between the several bloods. We cannot, for instance, 

 in the case when we are dealing with a batch of sera, of which the strongest 

 is competent to kill 6,000,000 typhoid bacilli, while the weakest is able to 

 kill only 600,000 bacilli, expect to elicit any differences of power with a 

 suspension which contains no more than 600,000 bacilli. Nor could we, if 

 we employed a suspension containing only 3,000,000, hope to differentiate 

 between bloods that can kill 3,000,000 and bloods which can kill up to 

 6,000,000. 



In the same way, when we are dealing with a batch of sera, of which the 

 strongest would be competent to opsonise sufficient microbes to give an 

 average ingest of 10 bacilli per cell, and the weakest only enough to give an 

 average ingest of 2 "5 microbes per cell, we cannot expect to bring out any 

 differences between the bloods with a suspension which could provide at 

 most 2\5 microbes per cell. Nor again, if we employ an emulsion which 

 could not provide more than five bacilli per cell, could we hope to 

 differentiate between bloods which could be competent to opsonise sufficient 

 microbes to give a count of 5 per cell, and bloods which would be able to 

 opsonise sufficient microbes to give us a count of 10 bacilli per cell. 



It might, in view of this reasoning, seem as if the only satisfactory 

 suspension would in the bactericidal test above mentioned be a suspension 

 containing six or more millions of typhoid bacilli, and for the opsonic test a 

 suspension which would give an average ingest of 10 microbes per cell. But 

 this is not so. 



All that is required is that each suspension should contain a quantity of 

 receptors equal to that which will be contained in these suspensions of the 

 required strengths, and Wright and Windsor* have shown in connection with 

 the bactericidal power that if the bloods are partially depleted of their 

 bactericidal power by the addition of receptors in the form of dead typhoid 



* 'Journal of Hygiene,' Oct., 1902, vol. 2, No. 4, and ' Studies of Immunisation,' p. 45. 



