ELEMENTS IN ORGANIC COMPOUNDS 187 
Histidine, a-amino imidazol propionic acid. 
L | 
H—C—=C-0-C-07 08 
H—-N JN H H 
| 
H 
Proline, a-pyrrolidine carboxylic acid. 
HeC CHe 
| | ao 
i 
H 
That amino acids are utilized by bacteria has been pointed out in 
other places. The commercial peptones which are used in the prepara- 
tion of media are, among other things, mixtures of amino acids. The 
changes induced by bacteria on certain amino acids in the intestinal 
tract are discussed in that chapter. Raistrick (1917) has shown that 
the bacteria of the coli-typhi group are able to change histidine into 
urocanic acid (iminazolylacrylic acid). Most of the other amino acids 
may be changed by bacterial enzymes to smaller molecules. Bacterial 
changes induced in other amino acids have been discussed elsewhere in 
this book. 
Qualitative Analysis for the Elements in Organic Compounds. The 
inorganic elements may be detected by heating some of the sample on a 
piece of platinum foil or porcelain. During this ignition the organic 
clements are driven off. The organic elements are determined by 
ignition with sodium. It often happens that an element is present in 
both organic and inorganic forms. 
Inorganic Elements. The substance is ignited on a piece of platinum 
foil or porcelain until all of the organic portion is destroyed. If the 
sample chars during this procedure, the presence of an organic substance 
is shown. If an inorganic substance is shown in the charring it may 
further be determined by the procedures of qualitative analysis. 
Organic Elements. Place a small piece of sodium in an ignition 
tube about 4 ins. long. Incline the tube in a slanting position and 
