216 



VETERINARY BACTERIOLOGY 



dewdrop-like colonies upon the surface of the medium. Bouillon 

 is slightly clouded. Milk is acidified and coagulated. The 

 addition of glycerin, and particularly blood-serum, stimulates 

 growth in most media. 



Physiology. The optimum temperature is 37; little or no 

 growth will occur at lower temperatures. Desiccation for several 

 months, particularly in sputum, does not always kill the organ- 

 ism. Twelve hours' exposure to direct sunlight is fatal. Acids 

 are produced from many carbohydrates. 



Pathogenesis. The pneumococcus produces acute septicemia 



when injected into the 

 mouse, guinea-pig, or rab- 

 bit. The production of 

 typical pneumonia is at- 

 tended with difficulty, if, 

 indeed, it has been satis- 

 factorily demonstrated. Its 

 principal claim to recogni- 

 tion as the etiologic factor 

 in the disease rests upon 

 its presence in the lesions 

 and its general pathogenic 



relationship to animals. 

 Thg f h . . ; 



commonly present in the 

 sputum of normal individuals seems to ihdicate that there are 

 great differences in disease-producing power among different 

 strains. Whether or not the organism isolated by Mayer from 

 pneumonia in the horse is identical with this organism cannot at 

 present be determined, nor can its relationship to " Brustseuche " 

 be said to be satisfactorily proved. 



The tissues of the lung invaded by the organism become con- 

 gested, and blood-plasma is poured into the alveoli. The fib- 

 rinogen coagulates, and the lung becomes " hepatized," that 

 is, liver-like in consistency. Frequently there is more or less 

 hemorrhage, largely by diapedesis, and the lung becomes red- 

 dened. Later leukocytes, particularly the polymorphonuclear 

 type, invade, and the tissues become gray. Autolytic digestion 



- 

 agar plate 



