300 University of California Publications in Zoology  |Vou.9 
Our attention may now be directed to the fact that the data 
(and the curve constructed from them) giving the general average 
of weights for young weaned at twenty-one days show that no 
loss of weight took place at weaning. This indicates that the 
young have not been dependent upon milk for their growth. 
The method used in calculating the percentage increments 
brings out this point to best advantage. Each change is shown 
by the percentage of the weight at the previous weighing which 
has been gained or lost in the interval between weighings. 
The cases of Be, Bb and Ca show that the earlier the animal 
is weaned the greater is the percentage of weight lost. These 
percentages are 8.7, 5, and 3.6 respectively, and the ages at which 
they are weaned are 4, 6, and 7 days respectively. 
The food given the young ones after they were separated from 
the mother was the same as that given to the young weaned at 
twenty-one days and to the adults. It consisted of hay, barley, 
lettuce, cabbage, grass and water. The animals weaned at the 
times stated above were given a larger proportion of freshly cut 
grass, which they ate more readily than any other food given 
to them. 
No attempt was made to supply heat. The young guinea-pig 
weaned at four days spent the first night away from the mother 
in a temperature of almost 40° F. During the day, however, its 
box was placed in the sunlight. 
In these experiments an attempt was made to have conditions 
the same for the animals weaned early as for all the others. No 
milk was given them at all, the only difference in diet being the 
larger proportion of green food given the animals weaned before 
twenty-one days. 
SUMMARY 
The guinea-pig is born in a very mature state and begins to 
eat solid food very early. An examination of the mother’s milk 
shows it to be very low in proteins, carbohydrates and inorganic 
salts, so we conclude that a large part of these foods needed by it 
is obtained from the solid food it eats. The percentage of fat 
(45.8) in the guinea-pigs’ milk is very high. Since the young 
