salt in the cloaca or large intestine. NECHAY and LUTHERER (1968) compared the
composition of urin~ collected directly from the ureter of one kidney with that from
the other kidney after it has passed through the cloaca in the normal wa y. Reflux
of urine into the intestine was prevented with a ligature. Under such conditions
no movement of electrolytes, and only a minor passive transfer of water from hypotonic urine were observed. However, if the intestine is left in communication with
the cloaca (SKADHAUGE, 1968) it was found that dehydrated chickens reabsorbed
about 50% of the water and sodium which passed out of the ureters. In v iv o perfusion of the cloaca and large intestine was also performed by SKADHAUGE (1967),
and he was able to demonstrate the reabsorption of sodium and water from such
preparations. These processes were not altered by vasotocin.
The observations of SKADHAUGE on water and sodium reabsorption from the
fluid in the cloacal and intestinal regions of chickens, are consistent with the increased drinking observed by DICKER and HASLAM in birds with ureters transplanted out of the cloaca. They also can account for the excessive losses of sodium
observed by HART and ESSEX in such birds. The composition of the urine of birds,
or more specifically the domestic fowl, would thus appear to be modified after it
passes into the cloaca, but the actual site of the reabsorption is probably the coprodaeum and large intestine. The rate of absorption of sodium and chloride from this
region of the gut can be regulated, as it has been observed to decrease by 50% in
domestic fowl to which an excess of sodium chloride has been administerd (SKADHAUGE, 1967). Whether such processes are influenced by hormones is unknown.
Corticosteroids from the adrenal cortex are logical candidates for such an action,
but their possible action at such a site has not yet been examined in birds.
KNUT SCHMIDT-NIELSEN has suggested (SCHMIDT-NIELSEN et al. , 1963)
that the functions of the cloaca and the nasal salt glands (see next section) may
be integrated so as to conserve water. This would result from the ability of many
birds to secrete salts at far higher concentrations in the nasal gland fluids than in
the urine. Urinary salts and accompanying osmotic water can be reabsorbed from
the cloaca and large intestine, and then, as seems likely in birds with functioning
nasal glands, the salt ma y be excreted through this channel, at concentrations that
would spare more water than would be possible in urine.
3. Conservation and Excretion of Salts
The principal avenues for salt loss in birds are the kidneys, gut and nasal salt glands.
Birds lack sweat glands, and so are not subjected to the relatively large salt losses
that may thus occur through the skin of many mammals.
a) Kidneys
Unavoidable salt losses occur in the urine of birds, just as in mammals, but these
are probably also small.
The process of renal salt excretion has been examined in the domestic duck by
HOLMES, FLETCHER, and STEWART (1968). When these birds were given fresh water
120
composition of urin~ collected directly from the ureter of one kidney with that from
the other kidney after it has passed through the cloaca in the normal wa y. Reflux
of urine into the intestine was prevented with a ligature. Under such conditions
no movement of electrolytes, and only a minor passive transfer of water from hypotonic urine were observed. However, if the intestine is left in communication with
the cloaca (SKADHAUGE, 1968) it was found that dehydrated chickens reabsorbed
about 50% of the water and sodium which passed out of the ureters. In v iv o perfusion of the cloaca and large intestine was also performed by SKADHAUGE (1967),
and he was able to demonstrate the reabsorption of sodium and water from such
preparations. These processes were not altered by vasotocin.
The observations of SKADHAUGE on water and sodium reabsorption from the
fluid in the cloacal and intestinal regions of chickens, are consistent with the increased drinking observed by DICKER and HASLAM in birds with ureters transplanted out of the cloaca. They also can account for the excessive losses of sodium
observed by HART and ESSEX in such birds. The composition of the urine of birds,
or more specifically the domestic fowl, would thus appear to be modified after it
passes into the cloaca, but the actual site of the reabsorption is probably the coprodaeum and large intestine. The rate of absorption of sodium and chloride from this
region of the gut can be regulated, as it has been observed to decrease by 50% in
domestic fowl to which an excess of sodium chloride has been administerd (SKADHAUGE, 1967). Whether such processes are influenced by hormones is unknown.
Corticosteroids from the adrenal cortex are logical candidates for such an action,
but their possible action at such a site has not yet been examined in birds.
KNUT SCHMIDT-NIELSEN has suggested (SCHMIDT-NIELSEN et al. , 1963)
that the functions of the cloaca and the nasal salt glands (see next section) may
be integrated so as to conserve water. This would result from the ability of many
birds to secrete salts at far higher concentrations in the nasal gland fluids than in
the urine. Urinary salts and accompanying osmotic water can be reabsorbed from
the cloaca and large intestine, and then, as seems likely in birds with functioning
nasal glands, the salt ma y be excreted through this channel, at concentrations that
would spare more water than would be possible in urine.
3. Conservation and Excretion of Salts
The principal avenues for salt loss in birds are the kidneys, gut and nasal salt glands.
Birds lack sweat glands, and so are not subjected to the relatively large salt losses
that may thus occur through the skin of many mammals.
a) Kidneys
Unavoidable salt losses occur in the urine of birds, just as in mammals, but these
are probably also small.
The process of renal salt excretion has been examined in the domestic duck by
HOLMES, FLETCHER, and STEWART (1968). When these birds were given fresh water
120