618 



NON-PATHOGENIC MICROCOCCI. 



234. MICROCOCCUS AMYLOVORUS (Burrill). 



Synonym. Micrococcus of pear blight. 



Found in the diseased branches of pear trees affected with ' ' blight " 

 "fire blight." Discovered by Burrill (1878) and carefully studied by Ar- 

 thur (1886). 



Morphology. Oval cells, from 1 to 1.25 n long and 0.5 to 0.75 n broad; 

 usually solitary, often in pairs, and occasionally in a linear series of four. 

 In fluid culture media form zooglcea, which are spherical or oblong and may 

 be from thirty to forty /f long and twenty to thirty /j. broad ; these zoogloea 

 masses may be solitary, or united in pairs or short chains ; they are found es- 

 pecially upon the surface of the culture medium, and after a time present a 

 wrinkled appearance, giving some resemblance to the external surface of 

 the brain. 



Biological Characters. An aerobic, non-liquefying, motile micrococcus 

 (bacillus?). Grows in various media at the room temperature. According to 

 Arthur, this micrococcus exhibits active "swarming movements" when 

 undergoing rapid multiplication in a favorable medium : ' ' The bacteria move 

 rapidly back and forth, in and out, among each other, but never in a straight 

 line to any distance. " An infusion of potato constitutes a favorable cul- 

 ture medium. In this medium, at a temperature of 25 to 30 C., turbidity 

 commences in twenty-four hours and bubbles of carbon dioxide are given 

 off ; in forty -eight hours the liquid is entirely turbid and a thin, whitish pel- 

 licle has formed on the surface, at the same time a sediment commences to 

 form at the bottom of the tube. Upon the surface of nutrient gelatin de- 

 velopment is very scanty and scarcely perceptible. In the interior small, 

 punctif orm colonies are developed ; these are spherical or oval, and may at- 

 tain a diameter of 0.5 millimetre. Upon slices of unripe pear, in two or 

 three days, fine milky drops like beads of dew are developed. Upon potato 

 a thin, moist, somewhat yellowish layer is developed. 



The experiments of Bun-ill and o'f Arthur show that the disease known 

 as pear blight is produced by applying cultures of this ' ' micrococcus " to 

 healthy branches of the pear tree. 



235. ASCOCOCCUS BILLROTHII. 



Found by Billroth in putrefying 

 flesh infusion. 



Morphology. Small cocci, united 

 in peculiar colonies. Upon the sur- 

 face of liquid media form a cream- 

 like layer in which numerous small, 

 spherical or oval masses are seen. 

 Under the microscope these are seen 

 to consist of a jelly-like, cartilaginous, 

 extremely resistant envelope from 

 ten to fifteen ju. thick ; in the interior 

 of this one or more spherical or oval 

 masses of cocci are enclosed, which 

 are from twenty to seventy n or more 

 in diameter; the cocci are closely 

 crowded and united by an unusually 

 firm and scanty intercellular sub- 

 stance. 



Biological Characters. Aerobic. Grows at the room temperature. 

 Produces a strongly alkaline reaction in culture media, due to the develop- 

 ment of ammonia. According to Cohn, a greenish- white, slimy mass is de- 

 veloped upon slices of beet, and in the juice of the sugar beet it produces a 

 slimy fermentation. 



FIG. 209. ASCOCOCCUS Billrothii. 



