56 LABORATORY BACTERIOLOGY 



EXERCISE XV 



THE MORPHOLOGY OF STREPTOCOCCUS, MICROCOCCUS, 

 AND SARCINA 



84. Genera among bacteria are based on the gross mor- 

 phology of the organisms. This is very largely true of all clas- 

 sifications. It is highly important, therefore, that the generic 

 characters should be thoroughly learned. While the descrip- 

 tive differences between a micrococcus and a bacterium seem 

 to be clear, there are many organisms where it is not so easy 

 to decide in which genus to place them. The almost constant 

 appearance of unexpected bacteria in septic infections and in 

 diseased organs renders it exceedingly desirable that one 

 should understand the fundamental elements of classification. 

 We must remember that the problems of the practitioner are 

 not all centered about known pathogenic forms like the organ- 

 isms of tuberculosis and diphtheria ; but they have to do with 

 a great host of infecting bacteria, of which we know as yet but 

 very little. 



85. Work for this exercise. Carefully describe each of 

 the bouillon cultures made in Exercise XIV. 



Prepare and examine a hanging-drop preparation from each 

 of the cultures, and describe the appearance (form) of the 

 organisms in each. Indicate the morphologic characters by 

 which each genus can be differentiated from the others. 



Make a cover-glass preparation from each culture and stain 

 with an aqueous solution of methyl violet ( 38). Make 

 a careful microscopic examination of each preparation and 

 describe the bacteria in each. 



Make careful notes on the appearance of the bacteria in each 

 preparation and preserve a specimen of each to accompany 

 the notes. 



