THE INFECTIOUS DISEASES. 215 



use of centrifugated cultures of the organism, the reaction of agglutination can be ob- 

 tained ill much greater dilution than by the usual method. 1 



Cultures which have been reduced in virulence, so as not to cause early death by 

 septicaemia, may, when introduced into the trachea of rabbits, induce circumscribed 

 pneumonic lesions, especially if these animals are made vulnerable by cold or by other 

 agencies which impair the integrity of the blood or other tissues. Wadsworth has 

 shown that by partially immunizing rabbits to the pneumococcus, so that they do not 

 speedily die from septicaemia, and then introducing the virulent organism into the lungs 

 through the trachea, diffuse pneumonic lesions comparable to the lobar pneumonias of 

 man may be induced. 2 Different animal species vary in vulnerability to the pneu- 

 mococcus. 



This germ is the exclusive inciter of typical acute lobar pneumonia in 

 man. It appears to act, in part at least, by the development of an albu- 

 minous poison which has been tentatively called pneumotoxin. 3 It would 

 seem to be the pueuinotoxin which induces the symptoms in acute lobar 

 pneumonia indicative of systemic poisoning. 



For a more detailed description of these lesions of pneumonia, and an 

 account of other bacteria which may be present, see p. 489. 



In addition to its more common effect in inducing lobar pneumonia, 

 the pneumococcus is frequently the excitant of exudative inflammation in 

 other parts of the body, either in connection with or without a primary 

 lobar pneumonia. Thus it has been repeatedly found in pleuritis, otitis, 

 meningitis, empyema, pericarditis, endocarditis, and in peritonitis. It 

 has also been found in abscesses of the viscera and in exudative inflam- 

 mation of the joints. It may induce pseudomembranous inflammation 

 of the mucous membranes. 4 Leucocytosis usually accompanies infection 

 with the pueumococcas. 



It is a frequent inhabitant of the mouth, even in health. It has 

 been found in the mouths of about twenty per cent of healthy^persons 

 examined. It is thrown off in the sputum in lobar pneumonia, and no 

 doubt from these sources in the dried condition, as dust, furnishes the 

 infectious agent which in favoring conditions of the body lights up the 

 inflammatory process in the lungs. 5 



For staining the pneumococcus with its capsule the following method of Hiss 6 gives 

 the best results. Mix the exudate or culture containing the organism on the cover- 

 glass with a drop of blood-serum spread thin, dry and fix by heat. Add a few drops 

 of the following stain: Five or ten per cent solution of gentian violet (5 c.c. saturated 

 alcoholic solution of gentian violet, plus 95 c.c. distilled water). Heat gently until steam 



1 For details of this method seeWadsicortft, Journal of Medical Research, vol. x., p. 

 228. 



2 See references to experimental pneumonia, p. 500. 



3 The observations of the Klemperers and others suggest the possibility that at a 

 certain period of the disease the blood or body juices are capable of developing a sub- 

 stance antidotal to this pneumotoxin, the potency of the former being signalized by the 

 so-called "crisis." Satisfactory applications of this alleged "pneumonia antitoxin" in 

 therapeutics have not yet been made. 



4 See Carey and Lyon, Trans. Assn. Amer. Phys., vol. xvi., p. 379, Bibl. 



5 Ottolenghi, Centralbl. f. Bakteriologie, Abth. I., Bd. xxv., p. 120, 1899. Fora full 

 resume of the studies on the Diplococcus pneumonia? see Weic/iselbaum in Kolle and 

 Wassermann's "Handbuch der Mikroorganismen," Bd. ii., p. 189. 



6 See Hiss, preliminary communication, Science, March 7th, 1902, p. 367. 



