648 THE MENINGOCOCCUS 



2. Vitality and virulence. 



Vitality. At room temperature cultures die in from 4-6 days : in the ice 

 chest they become sterile in 36-48 hours. In early sub-cultures the Meningo- 

 coccus dies in 3-6 days, but after being resown several times the organism 

 may live in the incubator for as long as 3 months (Albrecht and Ghon). 



Cultures are sterilized in 5 minutes at 65 C., in a few minutes at 80 (X 

 and instantly at 100 C. : and are also sterilized by desiccation for 3 hours 

 at 20 C. 



Virulence. The virulence of the Meningococcus is very inconstant, different 

 strains presenting varying degrees of pathogenicity, and it does not appear 

 to be increased by passage through animals. 



The severity of the symptoms produced in the human subject by a given 

 strain of Meningococcus bears no relation to the virulence of that strain for 

 the lower animals. 



On account of the considerable variation in the virulence of different 

 strains of Meningococci most observers use strains from several sources in 

 immunizing animals for the preparation of antimeningococcal serum. 



3. Toxins. 



Cultures of the Meningococcus sterilized by heat kill susceptible animals 

 as easily as living cultures. Filtered cultures have no toxic properties 

 (Jundell, Albrecht and Ghon). Flexner has shown that an emulsion of 

 Meningococci sterilized with toluol and filtered to remove the bacteria is 

 toxic. 



Dopter from his experiments concludes that the toxin is an endotoxin and 

 that the Meningococcus secretes no soluble toxins. The toxin can be extracted 

 by autolysis by treating the bacteria with distilled water : solutions prepared 

 in this way are often used for immunizing animals and preparing anti- 

 meningococcal serum (vide infra). 



4. Immunization. Serum therapy. 



Ruppel immunizes rabbits by inoculating them sub-cutaneously first with 

 a non-virulent strain then with a strain known to be of high and constant 

 virulence. The serum of these animals has prophylactic properties (0'004 c.c. 

 protects against 100 lethal doses). Ruppel's investigations led Flexner, and 

 then other bacteriologists, to attempt the immunization of horses for -the 

 purpose of preparing a therapeutic serum : the various methods which have 

 been employed will be considered under three heads. 



A. Flexner immunizes horses by inoculating them sub-cutaneously first 

 with dead cultures, then with living cultures, an$ finally with an autolytic 

 extract obtained by making an emulsion of virulent cultures in water. 

 (Flexner in his earlier experiments inoculated the horses intra-venously but 

 this method was abandoned in favour of sub-cutaneous inoculation.) 



B. Kolle, Wassermann and Leber immunize three horses simultaneously. 



One is inoculated with cultures of a single strain of the Meningococcus. The first 

 inoculation given sub-cutaneously consists of one-half a 24-hour agar culture made 

 into an emulsion with normal saline solution and heated to 60 C. : the second of 

 a whole culture similarly treated : the third of one-half a living non-heated culture 

 and the fourth of a whole non-heated culture. Afterwards the horse is inoculated 

 intra-venously on successive occasions with one-half, one, two, three, and four 

 living cultures. 



A second horse is treated in a similar manner but with a mixture of 5 or 6 strains 

 of Meningococci from different sources. 



