670 AETHUE ISAAC KENDALL 



medium to which has been added merely a minimum of 0.5 per cent of 

 glucose. Here the broth is acid in reaction in place of slightly alkaline, 

 but otherwise it appears to be the same (Van Turenhout, Smith, Kendall). 

 Injected into guinea pigs, however, the glucose broth is found to be wholly 

 without toxicity. The simple addition of a small amount of glucose has 

 completely changed the character of the products formed as the result of 

 the growth of the diphtheria bacillus. Lactic and other acids are formed 

 under these conditions, but no soluble toxin. 



Indol Formation. The amount of indican excreted in the urine has 

 long been regarded by some observers (Combe, Bahr) as an index of the 

 intensity of that obscure clinical condition spoken of as "auto-intoxica- 

 tion." Irrespective of the clinical significance of urinary indican, how- 

 ever, the parent substance is indol (Kendall), an aromatic residue of the 

 amino acid tryptophan. In man, indol is produced from tryptophan in 

 the intestinal tract by the action of Bacillus coli, Bacillus proteus, and to a 

 lesser extent by other facultative proteolytic organisms, acting in the 

 absence of utilizable carbohydrates. The absorption of indol from the ali- 

 mentary canal, its oxidization in the liver, and its excretion and sig- 

 nificance are discussed later. 



The production of indol from tryptophan by cultures of B. coli, Bacil- 

 lus proteus, the cholera vibrio or other bacteria can be observed readily 

 in the test tube; the conditions favoring or preventing its formation are 

 easily controlled. Indol appears within twenty-four to forty-eight hours in 

 ordinary sugar-free nutrient broth containing tryptophan, such as that in 

 which the diphtheria bacillus produces toxin. Precisely as the addition of 

 glucose to plain nutrient broth prevented the formation of diphtheria toxin 

 by the diphtheria bacillus, so that addition of glucose to such broth pre- 

 vents the formation of indol by the colon bacillus, Bacillus proteus and the 

 cholera vibrio. In place of indol and other products of putrefaction, which 

 appear in sugar-free media of the kind described, the addition of glucose 

 so changes the products of metabolism of these organisms that only organic 

 acids as lactic and acetic are formed, together with carbon dioxid and 

 hydrogen ; in other words, the substitution of utilizable carbohydrate for 

 protein as a source of energy alters completely the nature of the products 

 formed. 



The Formation of Protein-Liquefying Enzymes. Bacillus proteus, 

 the cholera vibrio, and several other parasitic and, less commonly, patho- 

 genic bacteria, form soluble enzymes, much like trypsin in their protein- 

 digestive power, in sugar-free media. These enzymes may be obtained in a 

 reactive state, quite free from bacteria, by filtering the latter away (Fuhr- 

 mann). The germ-free filtrate is strongly proteolytic for a variety of 

 proteins, including gelatin, breaking the complex molecule into amino 

 acids and po-lypeptids. 



The addition of glucose to cultures of the cholera vibrio or Bacillus 



