PRODUCTS OF METABOLISM. 113 



but it requires the presence of carbon dioxide, which is reduced by the 

 hydrogen to formaldehyde. 



CO 2 + 4 H=HCOH+H 2 O. 



The formaldehyde is then used by this bacillus as a food and oxidized. 



The presence of traces of formaldehyde in the cultures can easily be 

 proved. 



PRODUCTS FROM NITROGENOUS COMPOUNDS. 



The products resulting from microbial action upon nitrogenous 

 compounds are largely unknown or poorly defined. They are very num- 

 erous and many of them are of such complex nature that they cannot be 

 determined accurately; even the testing for their presence or absence is 

 often very difficult. It is therefore utterly impossible and quite unneces- 

 sary to mention even all the known products and the equations of their 

 formation. The aim is to give a thorough understanding of the gradual 

 degradation of the protein molecules to smaller molecules of less com- 

 plex nature, until finally crystallizing bodies are reached. These are 

 well-defined chemical bodies and the further decompositions can be 

 followed more exactly by chemical methods. 



As in the preceding chapter, the most complex compounds will be 

 discussed first. The keratin bodies of hair, epidermis, horn, are absolutely 

 insoluble and only very few organisms can attack them. The products 

 have been studied but very little and do not seem to differ essentially 

 from the cleavage products of protein bodies. 



PROTEIN BODIES are as numerous as plants and animals. Each 

 species of organism seems to have its particular protein which differs 

 from that of other species. With the more highly developed organisms, 

 there are several distinctly different proteins found in the same individual 

 in different parts of the body. The chemical structure of the protein mole- 

 cule is not known. The constituents, carbon, oxygen, hydrogen, nitrogen, 

 and sometimes sulphur and phosphorus can be determined in their 

 relative amounts without, however, furnishing any knowledge of the 

 structure of the molecule. The molecular weight of proteins is estimated 

 to be at least 10,000, while the weight of the very large molecule of sac- 

 charose is only 342. The protein molecule can be broken up into smaller 

 8 



