IDENTIFICATION OF MENINGOCOCCUS 249 



majority of carriers the organism can be found for only a 

 comparatively short time — a few days even, or a week or two — 

 but in a small proportion it persists for months, these being 

 " chronic " carriers. Such individuals will, of course, act in 

 maintaining the source of the infection, and it appears that the 

 occurrence of an epidemic disease depends upon a dissemination 

 of the organism through the community as evidenced by a high 

 carrier rate, though the conditions which lead to the dissemina- 

 tion are not understood. Unfortunately we have at present no 

 ready means of estimating the relative virulence of meningococci 

 obtained from the naso-pharynx and from elsewhere. With 

 regard to the epidemiology two facts are of importance.- One 

 is that direct infection of a healthy individual from a patient 

 suffering from the disease is comparatively uncommon) though 

 it sometimes occurs ; the other is that it is rare for a known 

 carrier to develop the disease. On the other hand, there is 

 substantial evidence of persons being infected from carriers. 

 The facts mentioned would seem to show that the organism 

 is spread widely from individual to individual, in most cases 

 without result, but that when the organism reaches a susceptible 

 individual the disease may rapidly develop. 'No doubt the 

 number of the organisms in the naso-pharynx is a factor of 

 importance, heavy carriers being especially dangerous. It has 

 been stated by some observers that the presence of the 

 meningococcus leads to, or is associated with, pharyngeal 

 catarrh, and that this often precedes meningeal infection. 

 More extended observations, however, have thrown doubt on 

 this, as it is certainly the case at least that the organism may 

 abound in the naso-pharynx without the presence of catarrh or 

 any abnormality. Manifestly the act of coughing, however, 

 will aid in its diffusion when it. is present. 



Identification of the meningococcus. — In the case of meningitis, this 

 usually presents no difficulty, as the finding of a Gram-negative diplo- 

 coccus in the cerebro-spinal fluid is practically conclusive. In the case 

 of the naso-pharynx, however, the matter is quite different. Means must 

 be taken to distinguish the organism from others resembling it, which 

 occur in the situation. Till recently, the following points taken together 

 have been usually accepted as justifying a positive diagnosis : conformity 

 in the microscopic characters and in the appearance of the colonies with 

 those of the meningococcus, ready emulsilication in saline, absence of 

 growth on agar at 23° C, fermentation of glucose and maltose, and non- 

 fermentation of saccharose. Attempts have been made to obtain identifica- 

 tion by means of agglutination, andin this connection the work of Gordon 

 has been of high value. On examining meningococci from various cases 

 of meningitis, he found that a serum prepared by injecting any one strain 

 did not agglutinate all the strains separated. Proceeding further and 



