STREPTOCOCCUS AND MICROCOCCUS 45 



EXERCISE XV 



THE MORPHOLOGY OF STREPTOCOCCUS AND 

 MICROCOCCUS 



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

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

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

 characters should be thoroughly learned. While the descriptive 

 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 centred about known pathogenic forms like the 

 organisms 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. 



71. 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 firom each culture and stain 

 with an aqueous solution of methyl-violet. 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 notes. 



Include in the notes the generic characters of each of these 

 genera. 



