EGGS AND THEIR VALUE AS FOOD. 15 
ing purposes instead of the whole egg (see p. 13). The clarifying 
properties are, of course, due to the egg white and not to the shell. 
Eggs are also employed in the arts, for instance, the use of egg 
white in the manufacture of albumin paper and of egg-yolk oil in fin- 
ishing leather. 
DIGESTIBILITY OF EGGS. 
Eggs are commonly said to be very digestible, especially when 
raw or slightly cooked. Probably most persons would understand by 
this that they digest without giving rise to pain or other physical dis- 
comfort. This is undoubtedly true, but the word " digestible " has 
another meaning in most discussions of food values. It refers not 
only to the ease, but also to the thoroughness, of digestion — that is, 
to the total amount of material that the food gives up to the body in 
its passage through the digestive tract. The original nature and 
condition of a food, the method of cooking, and the quantity eaten 
at a given time are among the factors that determine the amount of 
any given material that can be digested, but, in general, it is fair to 
say that the variations are less than is commonly supposed, the quan- 
tity of undigested food excreted from the body being usually very 
small. 
Statements often far from accurate are frequently made with 
regard to the length of time required to digest different foods. Some 
of them are based on investigations (some old and some recent) which 
take into account chiefly the length of time food remains in the 
stomach, assuming that this represents digestion and forgetting that 
digestion in the intestines must also be considered. Other statements 
are based on artificial digestion experiments in which the food is sub- 
jected in the laboratory to the action of digestive ferments which 
occur in the body. It is probable, however, that all the conditions 
of digestibility in the body can not be reproduced in the laboratory, 
and, although the results obtained are interesting and often valuable, 
it is worthy of note that careful investigators are much slower to 
make sweeping deductions from them than are popular writers on 
the subject. 
As regards thoroughness of digestion, that is, the proportion of 
nutritive material the body retains from a given food, eggs rank high, 
reliable experiments having shown that, on an average, 97 per cent of 
the protein and 95 per cent of the fat are assimilated. 
The question as to whether eggs are more or less digestible raw. 
slightly cooked, or hard cooked has also been studied by a number of 
investigators, the results indicating that, while cooking makes some 
difference with the rate (as shown by test-tube work), it makes little 
with the thoroughness of digestion. Even as regards quickness of 
digestion there is little difference between raw and slightly cooked 
