FOREWORD 



In the introduction to one of his Lectures and Lay Sermons, 

 Huxley used an analogy aptly illustrating his subject, and 

 singularly fitting the purposes of the present undertaking: "Mer- 

 chants occasionally go through a wholesome, though troublesome 

 and not always satisfactory, process which they term 'taking 

 stock.' After all the excitement of speculation, the pleasure of 

 gain, and the pain of loss, the trader makes up his mind to face 

 facts and to learn the exact quantity and quality of his solid and 

 reliable possessions. The man of science does well sometimes to 

 imitate this procedure; and, forgetting for the time the importance 

 of his own small winnings, to re-examine the common stock in 

 trade, so that he may make sure how far the store of the bullion in 

 the cellar — on the faith of whose existence so much paper has been 

 circulating — is really the solid gold of truth." 



The present undertaking is not an inventory of small personal 

 winnings, but rather a re-examination of the circulating paper and 

 an attempted appraisal of the quantity and quality of the stored 

 bullion, done with a sense of humility before the importance and 

 magnitude of the task. Nor is this an original enterprise. There 

 are the familiar Rockefeller Institute Monograph, Number Seven, 

 the ample summary of Neufeld and Schnitzer, and the later sym- 

 posium in the British System of Bacteriology, but since their pub- 

 lication more gold has been mined, vastly enriching the common 

 stock. In drawing upon this stock for the purpose of learning bet- 

 ter ways of applying our knowledge to the discovery of means for 

 mitigating the ills inflicted upon man by Pneumococcus, the whole 

 storehouse has been ransacked for hidden or forgotten goods. To 

 sort out the accumulation of more than fifty years, to convert old 

 specie into modern currency, and finally to set a value on the 

 whole store has been a troublesome task which it is hoped may be 



