466 PATHOGENIC MICROORGANISMS 



type III is probably the most dangerous of the organisms, followed 

 closely by types II and I, in the order named, and that type IV 

 organisms have, as a rule, a less alarming prognosis. 



ANTIBODY FORMATION, IMMUNITY, AND SPECIFIC 



THERAPY 



Recovery from a spontaneous pneumococcus infection confers 

 immunity for only a short period. Two and three attacks of lobar 

 pneumonia in the same individual are not unusual, and it is uncer- 

 tain whether even a temporary immunity is acquired in such infec- 

 tions. Our recent knowledge of types has made it seem not 

 impossible that successive attacks of pneumonia may be due to 

 consecutive infection with different types of organisms, thus leaving 

 open the possibility of the acquisition of prolonged immunity. But 

 this seems doubtful in view of the fact that Chickering 73 and others 

 have seen individuals who have had four or five attacks within a 

 relatively short time. The point, at any rate, is by no means settled. 

 Active immunization of laboratory animals may be carried out by 

 various methods. The method usually followed is to begin by in- 

 jecting attenuated 74 or dead bacteria or bacterial extracts. Subse- 

 quent injections are than made with gradually increasing doses of 

 living, virulent microorganisms. Great care in increasing the dosage 

 should be exercised since the loss of an animal after two or three 

 weeks' treatment by a carelessly high dose of pneumococci is not 

 unusual. Wadsworth centrifugalizes freshly grown pneumococcus 

 cultures and to the pneumococcic sediment adds a definite quantity 

 of concentrated salt solution. At the end of 12 hours, the pneumo- 

 cocci are dead and considerable destruction of the cell-bodies has 

 taken place. Dilution with water until the solution equals 0.85 per 

 cent NaCl now prepares the emulsion for inoculation. The sera of 

 animals immunized with pneumococci contain active bactericidal 

 substances. 



Specific agglutinins in pneumococcus immune sera were first 

 thoroughly studied by Neufeld 75 and since then have been made the 



73 Clnickering Discussion on pneumonia N. Y. Academy of Medicine, April, 

 1920. 



74 Eadziewsky, Zeit. f. Hyg., xxxvii, 1901; Neufeld, Zeit. f. Hyg., xi, 1902. 

 78 Neufeld, loc. cit. 



