FOOD STUFFS 



55 



-\--\ (- = very luxuriant growth, liquid turbid with bacteria or a pellicle upon the 

 surface (cholera, />'. sttbtilis'), or deposit of bacteria at bottom of vessel 

 (anthrax). 



H \- = growth moderate, faint but distinct turbidity or a delicate pellicle. 

 + = feeble growth, liquid opalescent or turbidity visible only on shaking. 

 + ? = scarcely any growth. 

 O = no growth. 



The most conspicuous result that the table shows is the great difference 

 between B, anthracis and B. pyocyaneus. The former prospers only where 

 peptone is available as a source of nitrogen ( i and 2), the latter grows just 

 as well and exhibits its magnificent fluorescence upon nitre (12). In other 

 words B. anthracis is a 'peptone bacterium} B. pyocyanens a ' nitrate bac- 

 terium ' approaching the members of the prototrophic group in its physio- 

 logy. The latter, however, needs a special source of carbon, not being 

 able to assimilate the carbon dioxide of the air (14). There is another 

 numerous group of metatrophic forms which, given carbon in a suitable 

 form, can utilise the nitrogen of ammonia compounds, and thrive as well 

 as they do upon peptone. B. coli is one of these ' ammonia bacteria, and 

 also V. cholerae and B. subtilis. Others, B. typhi for instance, are ' amido- 

 bacteria ' ; they cannot assimilate the nitrogen of ammonia, but grow fairly 

 well upon amide bodies, such as asparagine and leucine. One fact must 

 not be lost sight of if the bacteria are classified in this way, according to 



