33 2 DIFFICULTIES OF THE PROBLEM 



determination of the opsonic index in which thick emulsions of 

 bacteria are used the leucocytes are often found absolutely packed 

 with streptococci or tubercle bacilli after a short incubation ; if 

 on the average 100 cocci are taken up, calculation will show that 

 the whole volume of blood might phagocyte 2,000,000,000,000 in 

 a few minutes. Tubercle bacilli are perhaps hardly so easily 

 taken up, but it is difficult to see how the comparatively moderate 

 number of these bacteria which gain access to the blood after the 

 rupture of a small caseous gland into a vein can escape immediate 

 phagocytosis : yet we have no reason to believe that this accident 

 often occurs without causing general tuberculosis. Perhaps a 

 more convincing example is given by determinations of the opsonic 

 index in septicaemia, where the bacteria e.g., streptococci are 

 known to be circulating in the blood. Here the opsonic index is 

 usually low (0-5 or less), but even then it is sufficient to enable the 

 leucocytes to take up an enormously greater number of bacteria 

 than we can discover in the blood. 



Similar phenomena occur in the case of bacteria which are com- 

 bated largely by means of bacteriolysins. Thus, normal blood 

 serum is markedly bactericidal to typhoid bacilli, yet infection 

 occurs, and many observers have noticed relapses when the 

 bacteriolytic power of the blood is extremely high. In these 

 cases, therefore, the bacteria can gain access to the blood (for 

 typhoid fever is always in part a septicaemia) in spite of barriers 

 which would appear unsurmountable. And we have already had 

 occasion to mention that anthrax may occur in animals the blood 

 serum of which is powerfully bactericidal ; the animals, indeed, 

 may be extremely susceptible. 



Before attempting to explain the apparent discrepancy, it must 

 be pointed out that, as a matter of fact, septicaemia is a rare 

 disease in proportion to the opportunities for its occurrence, and 

 that the continued presence of bacteria in the blood without a local 

 lesion from which they are constantly discharged is extremely 

 uncommon. Thus in diphtheria, tetanus, the staphylomycoses, 

 etc., in which we should imagine that there is every chance for 

 bacteriaemia to occur, it is practically unknown. It is common in 

 diseases like ulcerative endocarditis, the early stages of typhoid 

 fever, and in pneumonia, in which we have reason to believe that 

 there is a constant shower of organisms discharged from the local 

 lesion direct into the blood. Here, however, w T e can feel fairly 

 certain that the bacteria which we find in the blood are only there 



