238 PRACTICAL PHYSIOLOGY 



Bacterial Action. The conditions necessary for bacterial growth are very 

 favourable in the intestine. As a result of their growth, bacteria decompose 

 the food-stuffs and lead to the production of products in many cases the same 

 as those of the digestive juices, in other cases of a different nature. In the 

 small intestine the bacteria which are most active are those acting on carbo- 

 hydrates, whereas in the large intestine these are largely replaced by bacteria 

 acting on protein. 



Their action on proteins leads to the production of proteoses, peptones, 

 and -ammo acids, etc. So far their action corresponds to that of trypsin, 

 but they digest farther and produce a multitude of simple degradation pro- 

 ducts, such as ammonia, fatty acids, carbonic acid, etc., as well as a group of 

 substances belonging to the aromatic series. 



The aromatic bodies are arranged in two groups. The one contains phenol 



C 6 H 5 OH and its methyl derivative cresol C 6 H 4 <^Qjj 3 . These are produced 

 from tyrosine, which has the formula 



. CH(NH 2 ) . COOH. 



When this changes into cresol and phenol, the amino-propionic acid side-chain 

 loses, first its amino group as ammonia, and then its carboxyl and methyl 

 group are oxidised and given off as carbonic acid and water. 



The other group is more complex, and contains indol C 6 

 and its methyl derivative scatol 



These are derived from tryptophan (p. 310). 



Anaerobic bacteria first of all act on the tyrosine and tryptophan, and 

 split off from them the amino (NH 2 ) groups as NH 3 . After this has been 

 accomplished, aerobic organisms act on the remaining side chains yielding 

 carbon dioxide and water. 



Certain of these aromatic bodies especially scatol have a strong fsecal 

 odour which they impart to the faeces. Considerable proportions of them are, 

 however, absorbed into the blood and reappear in the urine as indoxyl and 

 scatoxyl in combination with sulphuric acid and alkalis as aromatic sulphates 

 (see p. 264). 



EXPERIMENT X. Preparation and reactions of Indol, Scatol and Phenol. 

 Prepare an artificial digestion mixture with pancreatic extract, or minced 

 pancreas, and allow it to incubate without the addition of an antiseptic, until 

 it has an intense and disagreeable odour. The digest is then acidified with 

 acetic acid and placed in a large flask connected with a Liebig condenser. 

 Distillation is continued as long as the distillate has a marked odour. (Indol 

 distils over much more quickly than scatol.) The following tests are then 

 applied to portions of the distillate : 



Indol. 1. Legal' s Test To a few c.c. of the solution in a test tube add a 

 few drops of sodium nitro-prusside solution and then ammonia till alkaline. 

 A deep reddish violet colour results, which changes to blue on acidifying with 

 acetic acid. 2. Add to a few c.c. of the liquid about 2 c.c. of each of the 

 following solutions : (i) Para-dimethyl-amino-benzaldehyde 4 parts, 95 per 

 cent, alcohol 380 parts, hydrochloric acid (cone.) 80 parts, (ii) Potassium 

 persulphate 2 grams in 100 c.c. water. A reddish pink colour results. 



Scatol. Warm some of the solution with an equal volume of strong sulphuric 

 acid. A red colour results. 



Phenol. Boil some of the solution with Millon's reagent. A red colour, but 

 no precipitate is formed (see Estimation of Phenol in Urine, p. 291). 



