CHAPTER XIV 



THE OPSONIC INDEX AND VACCINE THERAPY 



WEIGHT'S 1 investigations upon phagocytosis were, indirectly, 

 the outcome of his earlier work upon antityphoid vaccination. His 

 purpose .in these studies had been a purely practical one, and he 

 had attempted to obtain a guide for the dosage and the interval be- 

 tween injections by measuring the bactericidal and agglutinating 

 powers of the blood serum. In the case of typhoid immunization 

 this was indeed a practicable method of control, since the bacteri- 

 cidal power of the blood serum rose directly as the immunization of 

 the patient was attained. In the cases of many other bacteria, how- 

 ever, this method of study was not practicable, and Wright, as others 

 before him, did not find a regularly increased specific bactericidal 

 power in the blood sera of immunized animals or of patients con- 

 valescing from infections with such bacteria as the staphylococcus, 

 streptococcus, Micrococcus melitensis, the Bacillus pestis, and a num- 

 ber of others. In fact, together with Windsor, 2 he showed that nor- 

 mal human blood has practically no bactericidal power for pyogenic 

 staphylococci and that antistaphylococcus inoculations or recovery 

 from an infection do not result in the production of such proper- 

 ties in the serum. These determinations are practically identical 

 with Nuttall's 3 earlier studies on the same bacteria and, indeed, cor- 

 respond with the data obtained by Metchnikoff and his followers in 

 their work on anthrax infection. For, in discussing these investi- 

 gations, we saw that very often the serum of a comparatively resist- 

 ant animal is less potently bactericidal than that of a more suscep- 

 tible one. We need only recall the difference between rabbits and 

 dogs in this respect. The serum of the former is more strongly bac- 

 tericidal than that of the latter, and yet rabbits are the far more 

 susceptible animals. These relations have been studied with great 

 care, also, by Petterson. 4 It was logical in such cases to look for 

 the cause of resistance in the activity of the phagocytes, and this, 

 we have seen, Metchnikoff did successfully in a large series of cases, 

 both as regards natural and acquired immunity. 



1 Wright. Lancet, 1902; Practitioner, Vol. 72, 1904. 



2 Wright and Windsor. Jour, of Hyg., Vol. 2, 1902 ; and Wright, 

 Lancet, 1900 and 1901. 



3 Nuttall. Zeitschr. f. Hyg., Vol. 4, 1888. 



4 Petterson. Centralbl. f. Bakt., Vol. 39. 



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