A comparison of the osmotic pressures along the digestive tract of the domestic fowl and the rabbit

1. The osmotic pressures of the contents of the alimentary tract from the adult hen and cockerel and rabbit were measured.

2. In the rabbit osmolality of the fluids from the different segments of the digestive tract was similar (331 ± 12 mOsm) and slightly hypertonic to blood plasma (297 ± 0.12 mOsm).

3. In the hen osmotic pressures were: crop 537, gizzard 312, duodenum 571, proximal jejunum 650, distal jejunum 573, proximal ileum 514 and distal ileum 451 mOsm. Only osmolality of the crop contents was influenced by egg formation.

4. In the cockerel osmotic pressure in the alimentary tract followed the same pattern as the hen and was modified by the time of day.

5. Plasma osmolality in the fowl was about 320 mOsm. Absorption of water across the proximal jejunum is achieved therefore against a gradient of about 330 mOsm in the female and 420 mOsm in the male fowl.