staining 445 



with immune serum. Recent researches make it certain that some 

 of the organisms formerly looked upon as pneumococci are different 

 and perhaps harmless. The pneumococcus is a purely parasitic, 

 pathogenic organism, best known to us in croupous pneumonia, 

 where it. is present in the lungs, sputum, and blood. It may be 

 found in the saliva of a large number of healthy persons (Parke 

 and Williams*), especially during the winter months (Longcope and 

 Foxf), and the inoculation of human saliva into rabbits frequently 

 causes septicemia in which the pneumococci are abundant in the 

 blood and tissues. Its frequent occurrence in the saliva led Flugge 

 to describe it as Bacillus septicus sputigenus. It is occasionally 

 found in inflammatory lesions other than pneumonia, as will be 

 pointed out below. 



Morphology. — The organism is variable in morphology. When 

 grown in bouillon it appears oval, has a pronounced disposition to 

 occur in pairs, and not infrequently forms chains of five or six mem- 

 bers, so that some have been disposed to look upon it as a streptococ- 

 cus (Gamal^ia). In the fibrinous exudate from croupous pneumonia, 

 in the rusty sputum, and in the blood of rabbits and mice, the organ- 

 isms occur in pairs, have a lanceolate shape, the pointed ends 

 usually being approximated, and are usually surrounded by a distinct 

 halo or capsule of clear, colorless, homogeneous material, thought by 

 some to be a swollen cell-wall, by others a mucus-like secretion 

 given off by the cells. When grown in culture-media, especially 

 upon solid media, the capsules are not apparent. The elongate 

 form has led Migulat to describe it under the name Bacterium 

 pneumoniae. 



The organism measures about i /i in greatest diameter, is without 

 motility, has no flagella and forms no spores. 



Staining. — It stains weU with the ordinary solutions of the anilin 

 dyes, and gives most beautiful pictures in blood and tissues when 

 stained by Gram's and Weigert's methods. 



To demonstrate the capsules, the glacial acetic acid method of 

 Welch§ may be used. The cover-glass is spread with a thin film of 

 the material to be examined, which is dried and fixed as usual. 

 Glacial acetic acid is dropped upon it for an instant, poured (not 

 washed) off, and at once followed by anilin-water gentian violet, in 

 which the staining continues several minutes, the stain being poured 

 off and replaced several times until the acid has all been removed. 



Finally, the preparation is washed in water containing i or 2 per 

 cent, of sodium chlorid, and may be examined at once in the salt 

 solution, or mounted in balsam after drying. The capsules are more 

 distinct when the examination is made in water. 



* "Jour. Exp. Med.," Aug. 7, 1905, vii, p. 403. 



T ibm., p. 430. 



I "System der Bakterien," Jena, igoo, p. 347. 



§ "Bull, of the Johns Hopkins Hospital," Dec, 1892, p. 128. 



