44 LABORATORY BACTERIOLOGY , 



I. Cell division always only in I plane . .1. Streptothrix. 

 II. Cell division in 3 planes previous to 

 the formation of conidia. 

 (i) Cells surrounded by a very delicate, 



scarcely visible sheath (marine) . 2. Phragmidiothrix. 

 (2) Sheath clearly visible (in fresh 



water) 3. Crenothrix. 



b. Cell threads branched (pseudo 



branches) 4. Cladothrix. 



Cell contents containing sulphur gran- 

 ules S- Thiothrix. 



5- 



Only I genus known (^Beggtatoa Trev.), which is scarcely sepa- 

 rable from Oscillaria. Character as given under the family. 



Of these genera Streptococcus, Micrococcus, Bacterium, 

 Bacillus, Microspira, and Spirillum contain the most important 

 of the pathogenic bacteria. The familiar genus Staphylococcus 

 of older classifications is included in the genus Micrococcus by 

 Migula. It is important that the distinguishing characters of 

 these genera be thoroughly learned. 



References. — Migula, Die natiirlichen Pflanzenfamilien, Liefe- 

 rung 129, Leipsic, 1896. Migula, System der Bakterien, 1897. 

 Fischer, Jahrbucher fiir wissenschaftliche Botanik, Band XXVII., 

 Erstes Heft. 



69. Work for this Exercise. — Read the references on the 

 morphology and classification of bacteria. 



Learn from the text-books and lecture notes the more essen- 

 tial elements in the structure of bacteria. 



Inoculate a tube of bouillon, one of agar, and one of gelatin 

 (from cultures which will be furnished) with each of the follow- 

 ing genera of bacteria. 



V A streptococcus . . . Streptococcus .... 

 ,, A micrococcus . . . Micrococcus 



