THE SAPROGENIC AND SAPROPHILIC BACTERIA 223 



faction of these amino acids, various gases, such as hydrogen, 

 marsh gas, ammonia, and carbon dioxide, are evolved. Ace- 

 tone is, in all probability, also formed from these amino 

 acids. 



From the diamino acids (hexone bases) some very interest- 

 ing substances are formed. These substances diamins 

 are formed by bacterial action, and are characterized by the 

 fact that they retain the NH 2 group, instead of splitting it off 

 as in the foregoing case. These substances are called ptomains, 

 and frequently, on absorption, produce serious intoxications 

 in the animal body. They will be discussed in Chapter 

 XXII. Not all ptomains are produced from this group. One 

 of the principal ones produced is putrescin (NH 2 (CH 2 )2NH 4 ). 



The aromatic substances of the protein molecule are phenyl- 

 alanin, tryptophan, and tyrosin. There are various sub- 

 stances formed from these bodies. Among those produced 

 are indol, cresol, and phenol from tyrosin; indol-propionic 

 acid, indol-acetic acid from tryptophan, and from these skatol 

 and indol. In intestinal putrefaction, the indol and skatol are 

 absorbed, oxidized, and combined with sulphuric or glycuronic 

 acid, and appear in the urine as the so-called ethereal sul- 

 phates. 



From the principal sulphur constituent of the protein 

 molecule, cystin, methyl mercaptan (CH 3 SH), ethyl mercap- 

 tan (C 2 H 5 SH), ethyl sulphide ((C 2 H5)S 2 ), and large amounts of 

 hydrogen sulphide (H 2 S) are produced. Hydrogen sulphide, 

 together with indol and skatol, are largely responsible for the 



