PRODUCTS OF MICROBIAL ACTIVITIES 243 



NH 3 and H2SO4. The nitrogen is never changed to any oxidation 

 product, but is found as NH 3 , while the sulphur is oxidized. 



Incomplete oxidation is caused by other bacteria, and perhaps molds 

 and yeasts. Quite a large number of organisms live on sugar-free 

 media if they have oxygen, but they do not oxidize their food com- 

 pletely. We can distinguish at least three different groups of micro- 

 organisms here. 



B. proteus is the collective name for a number of closely related 

 forms which belong to the most common organisms found on decaying 

 organic matter, especially when protein is abundant. They produce 

 leucin, tyrosin and tryptophane, but no skatol, or phenol. Tndol 

 and hydrogen sulphide are formed in certain media. Less important, 

 but also very common are the pigment-forming rods among which B. 

 fluorescent, B. prodigiosus, Ps. pyocyanea are the best-known repre- 

 sentatives. Their metabolism is a little different; amins and ammonia 

 are formed, while hydrogen sulphide, phenol and indol are absent. 

 As a third group, B. coli may be mentioned which forms indol, but no 

 ammonia from peptone, and whose proteolytic powers are very weak 

 as it does not even liquefy gelatin. 



Anaerobic decomposition of proteins is limited to very few species; 

 there is a great difference in the availability of proteins and of carbo- 

 hydrates as a source of energy, protein being available only to a few 

 species, most of^these preferring carbohydrates if they are present 

 together with protein. B. putrificus is the main representative, but 

 other forms exist. B. putrificus is strictly anaerobic, and a spore former, 

 very common in nature. Among the products are skatol, hydrogen 

 sulphide, ammonia and other very offensive compounds. 



UREA, URIC ACID, HIPPURIC ACID, are the end products of protein 

 metabolism of the higher animals. The decomposition of urea to 

 ammonium carbonate has been mentioned in several places, mainly 

 on page 202. It is a simple hydrolysis 



CO(NH 2 ) 2 + 2 H 2 = (NH 4 ) 2 C0 3 . 



This change can be brought about by only a few bacteria which are 

 commonly grouped together as "urea bacteria." These organisms 

 have hardly anything else in common, however, and the group is not a 

 well-defined one. There are rods and coccus forms, motile and non- 

 motile organisms, spore-formers and non-spore formers, and even molds 



