HOST RESPONSE TO ANTIGENIC ACTION 471 



pneumococcal products is bewildering, and from the data as pre- 

 sented it is difficult to gain a clear conception of the true signifi- 

 cance of specific skin tests in health, during pneumococcal infec- 

 tion, and in pneumonia patients receiving specific serum therapy. 

 The primary purpose of the authors of the present volume has 

 been to recite the many observations as they have been reported in 

 the literature in order that no contributions, whatever might be 

 their value, should be neglected. It should be borne in mind that in 

 many of the reports abstracted the materials employed for testing 

 skin reactivity were frequently mixtures of the native constituents 

 in more or less altered form of Pneumococcus, and of autolytic or 

 metabolic products of the cell. It is not surprising therefore that 

 the skin both of healthy persons and of pneumonic patients should 

 display a diversity of reactive manifestations following the intra- 

 dermal injection of bacterial suspensions in different stages of 

 autolysis, or of extracts or filtrates of pneumococci. Observations 

 of this nature, having been cited, may now be partly disregarded 

 and the discussion confined to the action of the more tangible, iso- 

 lated components of Pneumococcus. 



To arrive at the true significance of cutaneous reactions in hu- 

 man beings following the intradermal introduction of pneumococ- 

 cal materials it is necessary to consider the action of the separate 

 constituents of the pneumococcal cell employed in a comparatively 

 pure state and to determine as far as possible the experience of the 

 subject tested in regard to past or present pneumococcal infection. 



With improved methods in the preparation of bacterial protein 

 and somatic and capsular polysaccharides, antigens are now avail- 

 able for an analytical study of skin tests, but it is not always pos- 

 sible to ascertain the immunological condition in respect to Pneu- 

 mococcus of the person to be tested. 



A positive cutaneous reaction to the protein fraction of Pneu- 

 mococcus may be elicited by the appropriate injection of the anti- 

 gen into the skin of individuals who give no history of pneumonia. 

 In patients ill with the disease a similar injection gives a negative 



