DIPLOCOCCUS PNEUMONIA 363 



strains. Attempts to demonstrate by the production of antitoxin 

 the specific nature of the feeble poisons obtained have also met with 

 failure. Isaeff/ though confirming the feeble toxicity of fluid cultures, 

 made the interesting observation that a filtrate of the blood of pneumo- 

 coccus-infected rabbits contained a poison often more potent than that 

 obtained in culture filtrates. Carnot and Fournier ^ obtained a poison 

 of distinct though feeble potency by dialysis of pneumococcus cultures. 



The general failure, however, to procure strong soluble poisons from 

 cultures, gives weight to the assumption that the most potent toxic 

 products of pneumococci are in the nature of endotoxins and closely 

 bound to the cell-bodies themselves. This assumption is borne out by 

 the more recent experiments of Macfadyen.^ This author obtained 

 acutely poisonous substances from pneumococci by trituration of the 

 organisms after freezing, and extracting them with a one 1 : 1,000 

 caustic potash solution. With the filtrates of these extracts he was able 

 to cause rapid death in rabbits and guinea-pigs by the use of doses not 

 exceeding 0.5 to 1 c.c. He found, furthermore, a striking parallelism 

 between the degree of toxicity and the virulence of the extracted culture. 



Immunization. — Recovery from a spontaneous pneumococcus in- 

 fection confers immunity for only a short period. Two and three 

 attacks of lobar pneumonia in the same individual are not unusual, 

 and it is uncertain whether even a temporary immunity is acquired 

 in such infections. Active immunization of laboratory animals may 

 be carried out by various methods. The method usually followed is 

 to begin by injecting attenuated * or dead bacteria or bacterial ex- 

 tracts. Subsequent injections are then made with gradually increas- 

 ing 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 has recommended the following method for 

 preparing pneumococci for the first injections in immunizing rabbits. 

 Freshly grown pneumococcus cultures are centrifugalized, and the 

 supernatant bouillon is thoroughly decanted. To the pneumococcic 

 sediment a definite quantity of concentrated salt solution is added, and 

 the mixture is allowed to stand over night. At the end of this time, the 

 pneumococci are dead and considerable destruction of the cell-bodies 



> Isaeff, Ann. de I'inst. Pasteur, vii, 1893. 

 2 Carnot et Fournier, Arch, de m^d. exp6r., 1900. 

 'Macfadyen, Brit. Med. Jour., ii, 1906. 



* Radziewsky, Zeit. f. Hyg., xxxvii, 1901; Neufeld, Zeit. f. Hyg., xi, 1902. 

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