342 University of California Publications in Zoology [Vou.9 
guinea-pig picks up its own food by the mother’s side. The milk 
in this case plays but a secondary part therefore in its nutrition 
and only supplhes a welcome addition to the vegetable food so 
deficient in fat.”’ 
Only in one instance have I observed a young guinea-pig eat 
vegetable food during the first day after birth. This animal ate 
hay when about eighteen hours old. Upon two other oceasions 
I observed the young eat hay when forty-six and forty-eight 
hours old. 
Let us consider at this point the composition of the milk of 
this animal, and its probable relation to early weaning. In 
doing this a comparison of the milk of the guinea-pig with that 
of the rabbit is helpful. From table I (Bunge, 1902, table pp. 
104-105) we observe that rabbit’s milk is higher in protein, sugar 
and inorganic salts (ash) than the milk of the guinea-pig. These 
tissue- and bone-forming foods are needed by the young rabbit 
after birth in order to reach a stage of growth which is attained 
by the guinea-pig in utero. These same foods are supplied by 
the mother to the latter animal before parturition. 
TABLE I 
One hundred parts of Milk contain: 
Guinea-_ Ele- Rein- Por- 
Human Dog _ Rabbit pig phant Horse Goat deer Camel poise 
Casein 1.2 BE, eee RS reas 1,2 3.2 Bian 6 eee 
Albumin 0.5 OS Vere 0S ee ee 0.8 fail DQ) Wem 
Total Proteids isi veal 15.5 11.2 3.1 2.0 4.3 10.4 4.0 7.6 
Fat 3.8 12.5 10.5 45.8 19.6 1.2 4.8 wel 3.1 43.8 
Sugar of Milk 6.0 3.5 2.0 ie3} 8.8 oT 4.5 2.8 BiG zee 
Ash 0.2 1.3 2. 0.6 0.7 0.4 0.9 1.5 0.8 0.5 
The most striking comparison, however, is between the pro- 
portions of fat which the milks of the two rodents contain. The 
milk of the guinea-pig contains, in 100 parts, 45.8 parts of fat, 
while that of the rabbit has only 10.5 parts of fat. The table 
shows further that the milk of the porpoise has 43.8 parts of fat, 
this marine mammal ranking below the guinea-pig in the fat- 
content of its milk. 
