170 BACTERIOLOGY FOR NURSES 



mercuric chloride or 1 to 100 solution of carbolic acid. Its low 

 resistance to influences outside of the body, together with the 

 fact that it has not been demonstrated in the air or dust, is an 

 evidence of its parasitic nature. 



Pathogenesis. The organisms vary in their pathogenicity 

 for animals. Certain strains injected into the peritoneal cavity 

 of a guinea pig will produce a septicemia. Killed cultures may 

 also have a fatal effect, in which case death is probably due to a 

 bacterial poison of the nature of endotoxin, liberated by the dis- 

 integration of the organism. 



In human beings the course of the disease is very rapid; the 

 lesion is of a suppurative nature involving the meninges, the 

 base of the brain, and the surface of the spinal cord. During life 

 the surest method of diagnosis is the detection of the specific 

 microorganism in the spinal fluid withdrawn by means of a lumbar 

 puncture. In cases of meningitis due to the meningococcus, the 

 fluid appears somewhat cloudy, contains a high percentage of 

 polynuclear leukocytes, and the characteristic Gram negative 

 diplococci free or engulfed within the leukocytes. The mortality 

 without serum treatment is about 70 per cent. 



The organisms in all probability enter the body by way of the 

 nasopharynx, passing out of the nose and its adjoining cavities 

 along the path of the lymphatics toward the base of the skull. 

 They are present in great numbers in the nasal cavity during the 

 first twelve days of the disease, after which they disappear. 



Epidemics usually occur in the winter and spring months and 

 commence in localities where overcrowding is most likely. Be- 

 cause of the low vitality of the organism outside of the body 

 " carriers " may be largely responsible for the majority of out- 

 breaks, since the disease is undoubtedly transmitted from person 

 to person. During an epidemic not all the persons who harbor 

 the organism develop the disease ; the carriers have been shown 

 to outnumber the actual cases by ten to one. Apart from epi- 

 demics the meningococcus is rarely found on the membranes of 

 healthy persons, but evidently there are those who carry it always 

 and thus perpetuate the disease. 



