434
JOHAN B. STEEN
The central position of the rete in the swim bladder function is
clearly demonstrated by a comparison between the extent of its development and the depth at which the fish lives. Unfortunately, the only
parameters of the rete structure that have been sufficiently studied are
the length of the rete and the number of retial capillaries (Marshall,
1962). Deep sea fishes have longer retia than shallow water forms. This
indicates that the rete plays an essential role in gas deposition.
Before accepting the ccm explanation, three basic assumptions have
to be discussed. (1) The effect of the added substance must be present
at the pressure against which gas is to be deposited. (2) During gas
deposition the gas pressure must be higher in postrete venous blood
than in prerete arterial blood. ( 3 ) The rete must be impermeable to the
substance causing the increase in gas pressure.
1. PRESSURE-DEPENDENT SOLUBILITY
The most likely mechanism for a reduction in solubility is the addition of ions. The specific effect of H+ ions on the 0, capacity of blood
(Root effect) has been mentioned earlier. In many fishes the effect does
not persist to a Po, which is known to be present in their swim bladders.
The effect of ions on the physical solubility will not, however, be influenced by the partial pressure of the gas.
It seems, therefore, that an acid like lactic acid will fulfill the desired
requirements by salting out effect alone or, depending on the species,
in combination with a Bohr or Root effect.
2. ARTERIOVENOUS GAS GRADIENT
The Po, in arterial and venous blood at both poles of the rete of the
eel was estimated by Steen (1963~) from 0, content, pH, and hematocrit of appropriate blood samples. During established deposition of gas
the postrete venous Po, was found to be loaer than the prerete arterial.
Similar results were obtained by Steen and Iversen (1966) who measured
Po, polarographically.
3. IMPERMEABILITY FOR THE RETE TO ACIDS
In circulating blood CO, will be in equilibrium with H+ ions. Thus
a change in pH will cause a change in Pco,. Carbon dioxide is known to
pass biological membranes faster than 0, (about 20 times). If this
is the case also for rete tissue, then the ccm will be short-circuited. On
the other hand, ions are known to penetrate slower than water (about
10 times). Thus lactic acid deposited in the swim bladder capillaries
JOHAN B. STEEN
The central position of the rete in the swim bladder function is
clearly demonstrated by a comparison between the extent of its development and the depth at which the fish lives. Unfortunately, the only
parameters of the rete structure that have been sufficiently studied are
the length of the rete and the number of retial capillaries (Marshall,
1962). Deep sea fishes have longer retia than shallow water forms. This
indicates that the rete plays an essential role in gas deposition.
Before accepting the ccm explanation, three basic assumptions have
to be discussed. (1) The effect of the added substance must be present
at the pressure against which gas is to be deposited. (2) During gas
deposition the gas pressure must be higher in postrete venous blood
than in prerete arterial blood. ( 3 ) The rete must be impermeable to the
substance causing the increase in gas pressure.
1. PRESSURE-DEPENDENT SOLUBILITY
The most likely mechanism for a reduction in solubility is the addition of ions. The specific effect of H+ ions on the 0, capacity of blood
(Root effect) has been mentioned earlier. In many fishes the effect does
not persist to a Po, which is known to be present in their swim bladders.
The effect of ions on the physical solubility will not, however, be influenced by the partial pressure of the gas.
It seems, therefore, that an acid like lactic acid will fulfill the desired
requirements by salting out effect alone or, depending on the species,
in combination with a Bohr or Root effect.
2. ARTERIOVENOUS GAS GRADIENT
The Po, in arterial and venous blood at both poles of the rete of the
eel was estimated by Steen (1963~) from 0, content, pH, and hematocrit of appropriate blood samples. During established deposition of gas
the postrete venous Po, was found to be loaer than the prerete arterial.
Similar results were obtained by Steen and Iversen (1966) who measured
Po, polarographically.
3. IMPERMEABILITY FOR THE RETE TO ACIDS
In circulating blood CO, will be in equilibrium with H+ ions. Thus
a change in pH will cause a change in Pco,. Carbon dioxide is known to
pass biological membranes faster than 0, (about 20 times). If this
is the case also for rete tissue, then the ccm will be short-circuited. On
the other hand, ions are known to penetrate slower than water (about
10 times). Thus lactic acid deposited in the swim bladder capillaries