106 PROTEIN POISONS 



nitroprussiate added to a part of the clear filtrate, a beauti- 

 ful violet color is produced, indicating the presence of sulphur. 

 Also, if the other part of the clear filtrate be treated with a 

 lead acetate solution, lead sulphide is precipitated. If the 

 solution be acidified before lead acetate is added a faint 

 but unmistakable odor of hydrogen sulphide is detected. 

 It is known that sulphur may exist in the protein molecule 

 in at least two forms, one part being readily split off with 

 dilute alkali as a sulphide, the other being obtained only 

 when the disruption of the protein molecule is carried much 

 farther. It is still a question whether or not both of these 

 sulphur groups come from cystin. Since the nitroprussiate 

 reaction is very delicate, no conclusion as to the amount 

 of sulphur can be drawn from this test, and although a 

 good precipitate of lead sulphide is formed, the amount of 

 sulphur in the poison is probably not large, since Leach 

 failed entirely to find sulphur in the ash of the colon bacillus, 

 though both the cellular substance and the non-poisonous 

 portion, as well as the poison, respond to the nitroprussiate 

 test for sulphur and also give the lead sulphide precipitate 

 in the clear acidified filtrate from the fused mass. 



A solution of this toxic substance is not coagulated by 

 heat in acid, neutral, or alkaline solution, though, as already 

 stated, a few drops of a mineral acid added to an aqueous 

 solution causes the appearance of a considerable precipitate, 

 which is not soluble on heating or on the further addition 

 of acid. This precipitate is produced regardless of the 

 previous removal of the opalescence from the aqueous 

 solution. 



Among the metallic salts, copper sulphate produces no 

 precipitate and ferric chloride only on heating. Silver 

 nitrate naturally precipitates any trace of chlorides present, 

 but after the addition of an excess of ammonia there still 

 remains a small precipitate. Potassium ferrocyanide gives 

 a precipitate, also potassium bismuth iodide in acid solution. 

 Lead acetate, mercuric chloride, and platinum chloride 

 all produce heavy precipitates. With lead acetate and 

 mercuric chloride, however, after removal of lead and 



