MICROBIAL DISEASES OF MAN AND ANIMALS. 595 



of erysipelas is less easy because most of the organisms are found at the 

 margin of the lesion and are difficult to reach. 



In exudates a stained smear will usually demonstrate the chain-forming 

 coccus at once. 



The cocci vary in size from 0.4^ to i^. In shape the organisms may be rounded 

 or oval or with one aspect flattened when occurring in pairs. The chains may be long 

 or short and a grouping into pairs is frequent even within the chain. There are no 

 true spores developed and the organism is non-motile. Capsules are not found on the 

 majority of streptococci. Staining the organism is easily accomplished with the ordi- 

 nary aniline dyes. It is Gram-positive. The temperature range in which streptococci 

 are capable of growing is about from 15 to 35, the optimum temperature 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 feajture 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. facalis. 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 

 Cultivation is usually successful on the ordinary media. 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, leav- 

 ing 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 those 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 sometimes takes place. 

 Growth on potato is said not to take place, but in some cases an invisible growth 

 seems to occur. Loeffler'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 



