156 BACTERIA 



(Bacillus typhosus), epidemic meningitis or " spotted 

 fever " (Meningococcus), plague, cholera, diphtheria, 

 influenza, etc. 



PRACTICAL WORK. 

 Bacteria. 



Note that all bacteria are extremely small, and very careful 

 focussing with the high power is necessary to find them. 



(i) Bacteria in Potato Extract. — ^Mount a drop of the turbid 

 Kquid from the surface of water in which a shce of potato has 

 been soaking, put on a coverslip and observe the numerous 

 rod-shaped aerobic bacteria {Bacillus mesentericus) in motion ; 

 also from the deeper layer of water the rod shaped cells, tapering 

 at the ends of the anaerobic Clostridium buiyricum. Note the 

 different staining of the two with iodine. 



(2) Note the elongated form and the rapid spiral movements 

 (like those of eels) of the Spirilla from horse dung which has been 

 kept in water for a week. Kill with iodine solution and again 

 observe. 



(3) Bacillus subtilis (hay bacillus). — (a) Mount a drop of hot 

 water infusion of hay, and observe the delicate rod-shaped 

 bacilli in motion. (6) Examine a preparation showing the same 

 species fixed and stained. Compare their size with that of a 

 yeast cell by means of the micrometer eyepiece. 



(4) Stain a drop of each of the bacterial cultures (2) and (3a) 

 by the coverslip method used for yeast (p. 136 (4)). 



(5) Examine the sections of a nodule of the root of lupin (or 

 other leguminous plant), and note the " bacteroids " (dead 

 bacteria) in the central tissue. 



(6) Remove the cover from the dish of sterilised gelatine or 

 agar jelly provided, thus allowing the dust from the air to settle on 

 it. Replace the cover after twenty minutes, and label the dish 

 with your name. The dishes should be examined again after 

 a week's interval. 



Demonstration Specimens. — Examine carefully the demonstra- 

 tion slides, tubes and plates of various bacteria. 



[A few representative types of culture and stained preparations 

 of various pathogenic bacteria should be obtained for exhibition. 

 They can usually be borrowed from a pathological laboratory. 

 Cultures and slides of Bacillus tetani and B. anihracis, showing 

 spores of jB. tuberculosis, and of Staphylococcus and Streptococcus 

 are suggested as suitable.] 



The student should be warned not to handle the cultures. 



