44 STUDY AND IDENTIFICATION OF BACTERIA. 



them when turning over, it will be seen that they are different from the 

 tetrads which only divide in two directions of space. At times the 

 packet formation is not perfect and it will be difficult to distinguish 

 such as sarcinae. All sarcinae stain by Gram. If the staining of 

 sarcinse be too deep it may obscure the lines of cleavage. Sarcinaae are 

 nonmotile. 



Various sarcinae have been isolated from the stomach, especially 

 when there is stagnation of stomach contents. Sarcinae have also been 

 found in the intestines. In plates the S. lutea is frequently a contami- 

 nating organism, being rather constantly present in the air. The 

 demonstration of sarcina morphology should always be made from 

 liquid media, as bouillon. Urine makes an excellent medium. 



MICROCOCCUS FORMS. 



This grouping includes all cocci which do not show chain or packet 

 formation. It will be found convenient to divide them into two classes 

 according to their staining by Gram. The M. tetragenus, S. pyogenes 

 aureus and the pneumococcus stain by Gram, while the gonococcus 

 the meningococcus, the M. catarrhalis and the M. melitensis are 

 Gram negative. 



M. Tetragenus. This organism is frequently found associated 

 with other organisms in sputum, especially with tubercle and influenza 

 bacilli. The colonies are white, slightly smaller than staphylococci and 

 are quite viscid. 



It was formerly considered unimportant in disease, but the idea now 

 prevails that it is responsible for many abscesses about the mouth, 

 especially in connection with the teeth. Injected subcutaneously into 

 mice, it produces a septicaemia and death in three or four days. The 

 blood shows great numbers of encapsulated tetrads. It has been re- 

 ported twice as a cause of septicaemia in man. 



Staphylococci. To cocci dividing irregularly and usually forming 

 masses which are likened to clusters of grapes the term staphylococcus 

 is applied. While there have been experiments which show that by 

 selecting pale portions of a yellow colony, eventually a white colony 

 could be produced, yet, as a practical consideration, it is convenient 

 to consider at least two types of staphylococci: the staphylococcus 



