INTRODUCTION 



Pneumococcus is altogether an amazing cell. Tiny in size, sim- 

 ple in structure, frail in make-up, it possesses physiological 

 functions of great variety, performs biochemical feats of extraor- 

 dinary intricacy and, attacking man, sets up a stormy disease so 

 often fatal that it must be reckoned as one of the foremost causes 

 of human death. Furthermore, living or dead, whole or in part, on 

 entering the animal body Pneumococcus starts a train of impulses, 

 stimulating all the reactions grouped under those inclusive phe- 

 nomena known as immunity. 



Digesting foreign proteins, Pneumococcus rebuilds the frag- 

 ments into a new protein common to all types of the species ; split- 

 ting and consuming carbohydrates, from the simplest sugars to 

 the starch-like substances, inulin and glycogen, the cell synthesizes 

 the cleavage products of these same sugars into complex poly- 

 saccharides. These polysaccharides, chemically distinct and im- 

 munologically specific for the type, are built into a morphological 

 structure which forms a defensive armor against the destructive 

 forces of the animal body, and in a highly selective fashion de- 

 termines the precise nature of the immunological response each 

 separate type calls forth. 



Man has not been content to allow Pneumococcus to destroy 

 human life in an unrestrained way. The sanitarian has sought 

 hygienic and prophylactic measures to curb the incidence of acute 

 respiratory infections ; the pathologist has studied the anatomical 

 distribution and histological nature of pulmonary lesions in order 

 to gain fuller knowledge of the portal of entry and the pathway 

 of infection through the living tissues ; the epidemiologist has at- 

 tempted to track the mode of dissemination of the infectious agent 

 in the hope of breaking the vicious cycle of transmission from man 

 to man ; pending the discovery of specific therapy, the physician 

 has ameliorated suffering by symptomatic treatment and con- 



