334 MENINGOCOCCUS— GONOCOCCUS—CATARRHALIS GROUP 
with specific sera have attained some degree of success, although it 
is difficult to evaluate the protective process. This arises in part 
from the fact that the invasive power of the meningococcus appears 
to be a variable property of the living organism, quite distinct from 
the toxicity of the autolyzed bacteria. The latter is seemingly the 
destructive agent, once the coccus gains entrance to the cerebrospinal 
axis. 
The use of vaccines^ (either lipovaccines- or aqueous suspensions 
of the organisms, heated to 65° C. to restrict autolysis and preserved 
with phenol) for protective purposes has not been sufficiently studied 
to warrant definite statements'^ of its effectiveness. There is reason 
to believe that some degree of protection is aft'orded against the 
severity of the infection. Whether or not increased resistance to 
invasion by the microbe is thereby established is problematical. 
One of the most striking results of the intensive study of epidemic 
cerebrospinal meningitis was the discovery of typical meningococci 
in the nasopharynx of a very considerable number of apparently 
normal and healthy individuals, chiefly among those in actual contact 
with patients. These are meningococcus carriers. A smaller number 
of carriers occurs among individuals not in intimate association with 
patients, and fewer still in non-endemic or non-epidemic areas. The 
percentage of meningococcus carriers varies considerably. Dieudonne* 
found nearly 12 per cent of carriers in a garrison in Munich, where 
an epidemic of meningitis occurred. Bruns and Hohn^ found 465 
carriers among 3154 healthy individuals in a community wdiere the 
disease was epidemic. The percentage of carriers was greatest at 
the height of the disease. Among troops mobilized in barracks where 
there is overcrowding, the incidence of carriers may be even greater. 
During epidemic seasons the percentage of carriers in the civil popula- 
tion may be 3, 4, or even 5 per cent. 
The percentage of carriers and the incidence of cases usually run 
a more or less parallel course— the greater the percentage of carriers, 
the greater the number of cases. ^ In interepidemic periods the 
normal carrier rate in urban populations is said to be from 1 to 2 
per cent. The incidence in sparsely settled communities is unknown. 
More commonly, the carriers are temporary carriers. Smaller numbers 
become permanent carriers or intermittent carriers.^ 
Two principal factors play a part in the carrier incidence. A 
seasonal factor, in which epidemic and interepidemic periods are 
clearly recognizable, with a general increase and decrease of the carrier 
1 Davis: Jour. Iiifoc.Dis., 1907, 4, 558. 
2 Whitmorc: Jour. Am. Med. Assn., 1918, 70, 427. 
' Gates: .Jour. Exp. Med., 1918, 28, 449. 
4 Centralbl. f. BakterioL, orig., 1906, 41, 418. 
^ Klin .Tahrb., 1908, 18, 285. 
•> Nettler and T>evib: La Meningite Cerebrosiiinale, Paris, 1911. 
' Mayer and Waldmann: Miinchen. med. \Vchnschr., 1910, 57, 475. Mayer, 
Waldmann, Fiust and Griiber: Ibid., 1910, 57, 1584. 
