362 BACTERIA PATHOGENIC TO MAN 



dentated border. On the surface they are larger, appearing as pale 

 disks, almost transparent at the edges, but more compact toward the 

 centres, which are yellowish-gray in color. On blood agar or serum 

 agar the growth is much more luxuriant than on plain agar and larger 

 than the gonococcus. Not infrequently no growth is obtained when 

 the cerebrospinal fluid containing the diplococci is placed on plain 

 agar, and in rare instances no growth appears when serum agar is 

 used. Cultivated in artificial media while it often lives for weeks, it 

 may die within four days, and requires, therefore, to be transplanted 

 to fresh material at short intervals at least every two days. 



Resistance. It is readily killed by heat, sunlight, and drying. 



Pathogenesis. This organism does not show marked pathogenic power 

 for adult animals. It is most pathogenic for mice and guinea-pigs, less 

 so for rabbits and dogs. Subcutaneous injections in animals when large 

 cause death ; intrapleural or intraperitoneal inoculations in mice and 

 guinea-pigs, when given in large doses (y 1 ^ to J of a blood-serum cul- 

 ture), are usually fatal. Intravenous injections in rabbits have caused 

 the death of the animal, but no increase of diplococci in the blood or 

 characteristic pathological changes have been found as a result of the 

 injections. 



When mice are inoculated into the pleural or peritoneal cavities they 

 usually fall sick and die within thirty-six to forty-eight hours, showing 

 slight fibrinopurulent exudation. In the blood and enlarged spleen 

 diplococci are found in small numbers and mostly free; in the pleuritic 

 exudation they are present in considerable quantities, less so in the 

 peritoneal fluid, but then occurring in the interior of pus cells. 



Certain experiments made by Weichselbaum on dogs, though not 

 entirely successful, are interesting as showing the similarity of the disease 

 produced in them artificially with meningitis as occurring in man. The 

 three dogs, trephined and inoculated subdurally with 0.5 to 2 c.c. of a 

 fresh culture, all died : No. 1 within twelve hours, No. 2 in three days, 

 and No. 3 in twelve days. In Nos. 1 and 2 there were found hypersemia 

 of the meninges, with inflammatory softening of the brain at the point 

 of inoculation, which on nearer inspection proved to be a true encepha- 

 litic process. In dog No. 2, in which the disease was of longer duration, 

 these changes, were the most pronounced. Numerous diplococci were 

 observed in the sections removed, for the most part free, but some few 

 within the pus cells. In dog No. 3, in which the disease lasted twelve 

 days, a thick, reddish, purulent liquid was found between the dura mater 

 and the brain at the point of inoculation; in the brain itself an abscess 

 had formed, about the size of a hazel-nut, filled with tough, yellow pus, 

 while the abscess walls consisted of softened brain substance infiltrated 

 with numerous hemorrhagic deposits. The ventricles on that side 

 contained a cloudy, reddish fluid, with flocks of pus; but no diplococci 

 could be demonstrated in the blood or exudations. In our experience 

 injection of a recent culture into the spinal canal of very young puppies 

 is regularly followed by the results noted by Weichselbaum. Such 

 efi'ects are not observed in older dogs. 



