492 RECOGNITION OF BACTERIA. 



finely granular. In stained preparation, magnified a thou- 

 sand times, they are micrococci (probably Micrococcus 

 pyogenes albus, citreus, and aureus). The examination 

 must be carried further, as indicated on page 163. 



If there are only one or two colonies, — especially yellow 

 ones, — one may often recognize it as a contamination of 

 the plate by germs in the air, most often sarcinse. The 

 edges of the sarcina colonies, when magnified sixty times, 

 are coarsely granular or jagged. When magnified one 

 thousand times, packets of micrococci are seen. 



2. -Most minute, scarcely perceptible colonies, not ele- 

 vated, half a millimeter in diameter. When magnified 

 sixty times, extremely delicate, transparent, very delicately 

 punctate. The edges practically smooth (recalling gono- 

 coccus, Streptococcus lanceolatus, and Streptococcus pyo- 

 genes). In the last, one often observes upon ascites-agar 

 that chains of cocci grow out from the edge of the colony 

 in the form of the finest curling threads ! When the 

 stained preparation is examined under a magnification of 

 1000, the examination is to be continued according to 

 page 163, if cocci ; page 134, if streptococci ; page 195, if 

 bacilli. 



In order to render still more secure the diagnosis founded 

 upon morphologic and biologic peculiarities, several such 

 small colonies are taken up with a platinum loop and in- 

 troduced beneath the skin of a mouse, or this may be done 

 by employing more abundant infecting material (bouillon 

 culture). If we are dealing with a Streptococcus lanceo- 

 latus, we find in the blood and organs characteristic forms 

 of this variety with capsules. Smears from the blood and 

 organs are to be examined for the characteristic organisms 

 (Strept. pyogenes, Strep t. lanceolatus), and also new 

 smear inoculations made upon nutrient media. 



3. Tiny white to yellowish-white points, rather dense, and 

 just visible with certainty after twenty-four to forty-eight 

 hours. If the plates are kept longer, there is usually only 

 a slight increase in size, up to about 0.5 mm., and then, 

 with very few exceptions, they become no larger. They 

 are, however, always distinguished from those named 

 before by the tougher consistency. When magnified sixty 

 times, the border is ragged, often as if gnawed away, and 



