606 SCIENCE PROGRESS 



five years, and patients treated on these principles have given 

 consistently satisfactory results. The element of personal bias 

 is eliminated, because the estimations are made by observers 

 who do not know what cases they are investigating: this is 

 not insisted upon, but in practice each worker undertakes 

 haphazard a certain proportion of the day's work. And the 

 total estimations made now number tens of thousands. 



The most important points in connection with vaccine 

 therapy will best be made clear by a chronological survey ol 

 its development, as recorded in papers published by Wright 

 and his fellow workers. This method is selected because of 

 the authoritative character of these publications, and also 

 because the present writer has some: personal experience of 

 the observations. 



After their early observations that phagocytosis of bacteria 

 by leucocytes did not occur except in the presence of serum, 

 Wright and Douglas next proceeded to experiment with 

 different varieties of bacteria, and demonstrated that the opsonic 

 effect was produced on almost all ; two only, and those nearly 

 allied, out of ten organisms examined, proved refractory. 1 



The staphylococcus pyogenes was then examined in detail, when 

 it was found that persons suffering from pustular infection 

 showed a lower opsonic index to this organism than healthy 

 persons. Further, the pus derived from boils proved to have 

 less opsonic power than the blood. The patients were inocu- 

 lated with staphylococcus vaccines, and it was found that their 

 opsonic indices rose, concurrently with clinical improvement of 

 the lesions. 2 



The tubercle bacillus, the next investigated, presented great 

 technical difficulties, but when these were overcome, the same 

 facts became plain. The indices of patients with localised 

 tubercular disease were found to be lower than those of healthy 

 persons, and the indices obtained from pathological fluids, such 

 as serous effusions, were found to be lower still. Some cases 

 of localised tuberculosis were treated with inoculations of new 

 tuberculin, and considerable improvement was recorded. 3 



If these methods were to be of use in the diagnosis of 

 tubercular disease, it was clearly necessary to find out if normal 

 persons offer the same resistance to the tubercle bacillus — that 



1 Wright and Douglas, Proc. Roy Soc, vol. Ixxiii. 



2 Ibid. vol. Ixxiv. 3 Ibid. vol. lxxiv. 



