TEXT-BOOK OF BACTERIOLOGY. 345 



sule, transparent as glass, in which the bacteria are imbedded and 

 from which they stand out like the spots on dice; for the capsule 

 remains uncolored and appears as a transparent border. Some- 

 times only two or three cocci are thus cemented together, but this 

 is only when one of the members exceeds the others in size and 

 bulk, thus indicating that it is on the point of dividing and generat- 

 ing the missing cell. This striking kind of union at once resembles 

 the sarcina. On examining unstained objects, however, a hanging 

 blood-drop, etc., it will be seen that no division takes place here in 

 the third direction of space. 



This thickening of the membrane in the Micrococcus tetragenus 

 is almost exclusively found when it has thriven in an animal 

 organism. We, therefore, meet here with the features already' 

 observed in Fraenkel's and Friedlander's bacilli. 



The M. tetragenus belongs to the aerobic bacteria and is immo- 

 bile; it develops at ordinary and at incubator temperatures. 



It is easily stained with any anilin color and is an especially 

 favorable subject for Gram's double staining. 



On the plate the colonies appear at first as small white dots in 

 the depth of the gelatin, they advance to the surface rather rapidly, 

 and rise above the medium like arched elevations of a china lustre. 

 They do not, however, liquefy the gelatin or alter it in any other way. 

 Microscopically, round or oval, dense and yellowish-brown discs are 

 seen; they are of a slightly -granular structure; their borders are 

 mostly smooth and sharp-edged. 



In the test-tube there arise along the entire inoculation punc- 

 ture, thick, globular, dense, white masses and a moderately large 

 glistening coat on the free surface. 



On agar-agar and blood serum, a white, damp, extensive film is 

 formed. 



On potatoes there develops a thick, slimy coating which can be 

 taken off in long threads. 



The Micrococcus tetragenus is pathogenic for white mice and 

 Guinea-pigs, and house and field mice are usually susceptible, rab- 

 bits, etc., always. The white mice perish in three or four days 

 after the subcutaneous application of the bacteria. Guinea-pigs 

 endure larger quantities of the poison; it is best to inject directly 

 into the abdominal cavity. 



Post-mortem examination of mice shows a perceptible change : 

 whitish, rather extensive foci in the spleen (more rarely also in the 

 liver). Microscopically very large quantities of cocci are found in 

 the blood and all organs, having been distributed over the body 

 by the blood-current and, therefore, met with only in the vessels. 



