10. THE SWIM BLADDER AS A HYDROSTATIC ORGAN
433
In some fishes a Po2 of up to 140 atm did not increase the hemoglobin
saturation above that recorded at 20 atm, indicating strongly that
the acid blood suffers a permanently reduced O2 capacity (Root effect).
In response to reversal of the pH the blood regained normal O2 capacity,
thus showing that the Root effect is reversible. On the other hand, a
Root effect is not found in fishes lacking a bladder.
The proposal that the 0, present in the swim bladder is derived from
molecular 0, present in the water and transported in this form by Hb
is directly supported by the experiments of Scholander et al. (1956b).
Mass spectrometer analyses of gas from the bladder of codfish from
aquaria to which H,”O had been added revealed no trace of the heavy
isotope. It has further been shown by tracer experiments (Wittenberg,
1961) that there is no exchange of 0 atoms between 0, molecules as
these pass from the water via the blood to the bladder during gas deposition in the toadfish, Opsanus tau.
Acidification alone is, however, not sufficient to explain the high
Po, values found in deep sea fishes. Even if all the O2 of fish blood were
split off it would not raise the Po, to above some 5 atm.
B. Release of Inert Gases from Blood
As we have noticed in an earlier section the PN2 in the bladder may
also exceed that in the water. The mechanism of inert gas deposition is
thought to be based on release of some of the gas present in physical
solution in the blood. Koch (1934) pointed out that an acid added to
the blood would not only dissociate Hb02, it would also increase the
ionic strength of the blood and reduce its gas solubility. This type of
gas release will of course affect all gases and may be brought about
by any ion added to blood. It is commonly termed the “salting out”
effect. If half of the dissolved gas were salted out, the partial pressure
would double. Such an increase would, however, require an increase of
ionic strength far above that which is compatible with normal physiology.
C. Multiplication by the Rete
The notion that the primary gradient caused by acidification is multiplied by ccm in the rete receives support from the very existence of the
rete as well as from its unique architecture. This, together with the pH
sensitivity of Hb02, led Haldane (1922) to suggest that O2 is deposited
as a consequence to acidification and that the effect is possibly amplified
by circulation through the rete.
433
In some fishes a Po2 of up to 140 atm did not increase the hemoglobin
saturation above that recorded at 20 atm, indicating strongly that
the acid blood suffers a permanently reduced O2 capacity (Root effect).
In response to reversal of the pH the blood regained normal O2 capacity,
thus showing that the Root effect is reversible. On the other hand, a
Root effect is not found in fishes lacking a bladder.
The proposal that the 0, present in the swim bladder is derived from
molecular 0, present in the water and transported in this form by Hb
is directly supported by the experiments of Scholander et al. (1956b).
Mass spectrometer analyses of gas from the bladder of codfish from
aquaria to which H,”O had been added revealed no trace of the heavy
isotope. It has further been shown by tracer experiments (Wittenberg,
1961) that there is no exchange of 0 atoms between 0, molecules as
these pass from the water via the blood to the bladder during gas deposition in the toadfish, Opsanus tau.
Acidification alone is, however, not sufficient to explain the high
Po, values found in deep sea fishes. Even if all the O2 of fish blood were
split off it would not raise the Po, to above some 5 atm.
B. Release of Inert Gases from Blood
As we have noticed in an earlier section the PN2 in the bladder may
also exceed that in the water. The mechanism of inert gas deposition is
thought to be based on release of some of the gas present in physical
solution in the blood. Koch (1934) pointed out that an acid added to
the blood would not only dissociate Hb02, it would also increase the
ionic strength of the blood and reduce its gas solubility. This type of
gas release will of course affect all gases and may be brought about
by any ion added to blood. It is commonly termed the “salting out”
effect. If half of the dissolved gas were salted out, the partial pressure
would double. Such an increase would, however, require an increase of
ionic strength far above that which is compatible with normal physiology.
C. Multiplication by the Rete
The notion that the primary gradient caused by acidification is multiplied by ccm in the rete receives support from the very existence of the
rete as well as from its unique architecture. This, together with the pH
sensitivity of Hb02, led Haldane (1922) to suggest that O2 is deposited
as a consequence to acidification and that the effect is possibly amplified
by circulation through the rete.