THE STUDY OF BACTERIA 131 



14. Note the presence of condensation water, whether 

 a small or large amount is present. How does this affect 

 colony development? 



15. Draw and measure a typical surface and subsurface 

 colony produced by each organism. 



The form and size often vary with the physical con- 

 dition under which the colony grows or with physiological 

 conditions, i.e., the proximity of colonies producing poison- 

 ous metabolic products. 



16. Examine cultures three to six days old in hanging 

 drop for presence of spores. Spores may be seen free or 

 enclosed in the bacterial cells. They are easily distinguished 

 by their refractivity. Ordinary anilin dyes will not stain 

 them. 



17. Make a contrast spore stain of a spore-forming 

 organism. (For method see Exercise 29.) 



Draw and describe only the mature cultures of the last 

 six organisms (five to eight days old) . 



18. Make the indol, nitrate and ammonia tests also 

 on the mature cultures. 



19. In fermentation tube cultures note and record the 

 oxygen requirements of each organism; total per cent of 

 gas; ratio of CO2 : H2 and other gases. 



20. Test each organism after seven days for indol, 

 nitrate and ammonia production. The culture in Dun- 

 ham's peptone solution is tested for indol (for method 

 see Exercise 44). 



Divide the nitrate peptone solution culture into two parts; 

 test one for nitrates, the other for ammonia (for method 

 see Exercise 45). 



21. Prepare permanent stained preparations of one 

 Gram-positive and one Gram-negative organism. 



22. Making use of morphological and cultural charac- 

 teristics ascertained microscopically and by the various 

 cultural tests, identify each organism, using Chester's 

 Manual of Determinative Bacteriology for tracing out 



