/CH₃ / N--CH₃ \ \CH₃, a liquid, results when three hydrogens are similarly replaced. All three of these occur in herring brine and are responsible for the characteristic odor of this material. Putrescin and cadaverin--tetramethylene--diamine, and pentamethylenediamine respectively--occur generally in decomposing flesh, hence the names. They are only slightly poisonous. One of the highly poisonous ptomaines is neurin C₅H₁₃NO or C₂H₃N(CH₃)₃OH = trimethyl-vinyl ammonium hydroxide. This is a stronger base than ammonia, liberating it from its salts. Numerous other ptomaines have been isolated and described. These bodies were considered for a long time to be the cause of various kinds of “meat poisoning,” “ice cream poisoning,” “cheese poisoning,” etc. It is true that they may sometimes cause these conditions, but they are very much rarer than the laity generally believe. Most of the “meat poisonings” in America are due, not to ptomaines, but to infections with certain bacilli of the _Bacterium enteritidis_ group. Occasionally a case of poisoning by the true toxin (see Chapter XII) of _Clostridium botulinum_ occurs, and in recent years has become entirely too common due to insufficient heating of canned goods. _The boiling of such material will destroy this toxin. The safest rule to follow is not to eat any canned material that shows any departure from the normal in flavor, taste or consistency._ As ptomaines result from the putrefaction of proteins, so they are still further decomposed by bacteria and eventually the nitrogen is liberated either as free nitrogen or as ammonia. Another series of products are the so-called aromatic compounds--phenol (carbolic acid), various cresols, also indol and skatol or methyl indol (these two are largely responsible for the characteristic odor of human feces). All of these nitrogen compounds are attacked by bacteria and the nitrogen is eventually liberated, so far as it is not locked up in the bodies of the bacteria, as free nitrogen or as ammonia. The carbon which occurs in proteins accompanies the nitrogen in many of the above products, but also appears in nitrogen-free organic acids, aldehydes and alcohols which are all eventually split up, so that the carbon is changed to carbon dioxide or in the absence of oxygen partly to marsh gas. The intermediate changes which the sulphur in proteins undergoes are not known, but it is liberated as sulphuretted hydrogen (H₂S) or as various mercaptans (all foul-smelling), or is partially oxidized to sulphuric acid. Some of the H₂S and the sulphur of the mercaptans are oxidized by the sulphur bacteria to free sulphur and finally to sulphuric acid.