1044 FOODS AND FOOD ADULTERANTS. 



! 



number of species (18 out of 25 known) of the turaco, or plantain eater, 

 an African bird, are colored red by a pigment containing about 6 per 

 cent of copper. These birds undoubtedly derive their copper from 

 their food, and from its constant occurrence in their plumage it must 

 be a normal constituent of the vegetable foods upon which they live. 



In 1858 A. Dupre and Dr. Odling 1 investigated a large number of 

 common vegetable materials and foods for copper. In nearly all cases 

 the metal was found, though always in very minute quantity. Out of 

 22 samples of bread 21 contained traces ; 20 samples of flour were all 

 found to contain it, and the same was the case with 43 miscellaneous 

 samples, comprising wheat, barley, maize, wheat straw, barley straw, 

 turnips of different kinds, and beets. In 25 samples the metal was 

 estimated. The maximum amount found was in a sample of wheat ash, 

 being 0.024 part in 100 parts of ash. This corresponds to about 1,000 

 parts of fresh wheat, equivalent to about one part of copper oxid to 

 240,000 parts of wheat, in turn equivalent to something over 3 nig of 

 copper per kilo. A sample of turnip contained the minimum amount 

 determined, the copper as copper oxid amounting to about 1 part to 

 4,375,000 of the fresh turnip. When enough material was taken the cop- 

 per was almost always found. That naturally present, however, sel- 

 dom ever amounted to more than 1 part to 200,000 (5 mg per kilo). 

 Animal substances (29 samples) were also tested and nearly all yielded 

 the metal. Human liver showed 2 parts of copper oxid per million ; 

 sheeps' liver, in two cases, 50 parts 5 and kidneys, about 10 parts. 

 Dupr6 and Odling came to the conclusion that in the case of vegetable 

 foods the presence of more than 10 parts of copper per million of food 

 must be looked upon as an adulteration. Foj? green peas, however, 

 they placed the limit at 18 to 36 parts. The method of analysis 

 employed was to precipitate the copper on a platinum wire by a weak 

 galvanic current, redissolve in nitric acid, and finally weigh as copper 

 oxid. 



Many other chemists have sought to show the constant existence of 

 copper in animal and vegetable tissues, and a fairly large literature 

 on the subject has accumulated. It seems to be proved that copper 

 often occurs, but the proof adduced does not show at all that the metal 

 is a constant component of the tissues in question. The mere fact that 

 it is not found in many cases proves that it is not a normal constituent 

 of living tissues. The drift of the evidence seems to be that it was an 

 accidental ingredient in many cases where it has been found in tissues 

 from the higher animals and plants. That it is not always so is shown 

 by the case of the turaco. 



Copper is present in many soils, and since the metal forms no salts 

 which are particularly insoluble, it must often happen that plant roots 

 find dissolved copper presented to them, and no doubt they sometimes 

 absorb it. The amounts of copper found in common plants, however, 



Guy's Hospital Reports, 1858, 103, Analyst, 1878, 2, 1. 



