MICROBIAL DISEASES OF MAN AND DOMESTIC ANIMALS 797 



streptococci are capable of growing is about from 15 to 45, the optimum tem- 

 perature is about 37. Streptococci are, as a rule, aerobes and facultative anaerobes. 

 Strict anaerobic species are said to have been isolated from faeces. The reaction of 

 media should be slightly alkaline. Acid production is a striking feature of this 

 organism and has a decided inhibitive effect upon its growth. Concerning the 

 action on carbohydrates this organism typically forms acid from monosaccharides, 

 lactose, saccharose, and salicin. Gas is never produced. Nitrates are reduced by 

 some streptococci to nitrites. The production of hydrogen sulphide is characteristic 

 of some forms which have been grouped as Strept. fcecalis. No pigment is found 

 other than the slight brownish tinge seen in some gelatin cultures. Typically 

 actively haemolytic. This power may be lost on cultivation. The toxic products 

 of the streptococci have been the subject of a great deal of investigation, but few 

 definite facts have been discovered. When cultivated on plain nutrient agar the 

 growth is visible in eighteen to twenty-four hours as small round translucent finely 

 granular colonies, which possess an even or notched border, and a tendency to remain 

 discrete except when thickly sown. The center is thickened and the margins thinner. 

 In plain nutrient broth the majority of long-chained varieties produce at the bottom 

 and along the sides of the tube a granular deposit, or small flocculi or large flakes, 

 leaving the remainder of the broth clear. A few long-chained varieties cloud the 

 broth uniformly. The short-chained streptococci as a rule, produce a cloudiness in 

 the medium which remains for a number of days even though a finely granular 

 deposit accumulates at the bottom of the tube. On plates of plain nutrient gelatin 

 the colony formation remains the same as that on agar. In stab cultures a finely 

 granular filiform growth appears which later may have a beaded appearance and 

 sometimes a brownish color. The gelatin is not liquefied. Milk is a favorable 

 medium for the growth of streptococci and a strong acidity and coagulation some- 

 times takes place. Growth on potato is said not to take place, but in some cases 

 an invisible growth seems to occur. LoefHer's blood serum is also a favorable 

 medium. Streptococci, as a rule, die out rapidly in cultures due to the accumulation 

 of their own products. In pus, blood, sputum, etc., the organism may be found 

 alive after several weeks or even months at room temperature. The thermal death- 

 point is about 54 in ten minutes. Direct sunlight kills within a few hours, and 

 they are readily killed by many disinfectants. 



Entrance of streptococci is afforded by any break in the surface of 

 the body. A local suppuration may be the result or it may be followed 

 by a general septicaemic condition. 



In erysipelas some local injury is also probably necessary as a 

 starting-point. 



Following the local establishment of streptococci sufficient toxin 

 is elaborated to produce greater or less systemic disturbance. If a 

 septicaemia supervenes the poisoning becomes extreme and the organ- 

 isms are distributed throughout the body. 



Immunity following recovery from natural streptococcic infection 



