838 PLANTS USED BY INDIANS OF MENDOCINO COUNTY, CAL. 
The dough selected for acorn bread is mixed with red clay before it 
is baked, the proportion being about 1 pound of clay to 20 of dough. 
This clay, several Indians explained, makes the bread sweet. Others 
stated that it ‘tacted like yeast.” The mixture is placed on a bed of 
soaproot, oak, maple, or even poison-oak leaves, which in turn rests 
ona bed of rocks previously heated by a small fire. The dough is then 
covered with leaves and a layer of hot rocks and dirt and cooked 
gently in this primitive oven for about twelve hours, usually over 
night. When removed the next morning the bread, if previously 
mixed with clay, is as black as jet, and, while still fresh, has the cen- 
sistency of rather soft cheese. In the course of afew days it becomes 
hard, when, on account of the leaf impressions stamped upon it, it 
might easily be mistaken for a fossil-bearing piece of coal. It is not 
at all porous, being as heavy as so much cheese. It is remarkable for 
being sweet, for the original meal and even the soup are rather insipid. 
The sweet taste is very evident, and is due in great measure to the 
prolonged and gentle cooking, which, favored by the moisture of the 
dough, gradually converts some constituent of the meal into sugar, as 
in the case of camas bulbs, 
One or two specimens of bread observed, which were made without 
the addition of clay, were also sweet. These varied only in color. 
They were not black, but varied from light tan to dark, reddish brown. 
All were oily, and about equally heavy. It is evident, therefore, that 
neither of the above explanations given by the Indians for the use of 
the clay is satisfactory, 
Among the explanations given by others for the use of this material 
the following are of interest: The preference for black colors, as shown 
in the uniform practice of blackening basket materials, and in several 
ways; the absorption by the clay of the oil, which might otherwise be 
lost in cooking: the dilution of the bread, to make it last longer, or to 
assuage hunger temporarily, a purpose for which it is claimed by many 
persons clay is used by primitive people in tropical or subtropical 
countries throughout the world; ceremonial purposes; the killing of 
intestinal worms; for the arsenic contained in it: or, finally, for the 
bone-forming material it contains, this being held to be especially 
important in the case of people who get most of their nourishment 
from vegetable matter. It is not my desire to discuss here these vari- 
ous explanations, but I wish to give a scientific explanation which has 
suggested itself to me. It seems certain that the clay is used for a 
very scientific and useful purpose, and that is to convert the last. trace 
of tannin still remaining in the dough into an insoluble form. The 
black color is unquestionably due to the tasteless insoluble compound 
formed at the baking temperature, under the influence of air and moist- 
ure, by the action of the tannin of the acorn with the oxide of iron con- 
tained in the clay. An analysis of a sample of this clay, made by Dr. 
