GAS GLANDS OF SOME TELEOSTEAN FISHES. 233 



pigment contained in the red corpuscles is, as is well known, a 

 very loose one, and this loose combination is, according to modern 

 views, only maintained by the maximum partial pi-essure exerted 

 by the small amount of oxygen dissolved in the blood plasma. 

 Furthei', it is important to notice in connection with the present 

 subject that in the liberation of oxygen to the tissues of the body, 

 it is the oxygen dissolved in the plasma which is immediately 

 supplied to the tissues, and not the oxygen associated with the 

 hajnioglobin. The oxygen of the oxyhamioglobin compovmd only 

 becomes liberated as a consequence of the lowering of the partial 

 pressure of the plasma oxygen caused by tissue a,bsorj)tion and 

 when liberated meiely serves to replenish the plasma and is not 

 conveyed directly to the tissues, so that the plasma with its 

 limited solvent action on oxygen must be recognized as the all- 

 important intermediary between the store of oxygen combined 

 with the haemoglobin and the tissues. Now in the case of the 

 cells of the gas gland, already employed in pumping oxygen into 

 the bladder and certainly possessing all and moi'e than they 

 require for metabolic purposes, it is difficult to imagine that they 

 can absorb the oxygen dissolved in the pltisma in the manner 

 employed by ordinary tissue cells. Even if they are so able, the 

 small amount of oxygen so obtainable is quite insufficient for 

 their purposes, since the oxygen, unlike the nitrogen and carbon 

 dioxide, is required to be i^apidly produced in large quantities. 

 The only alternative is, then, for the gas gland cells to seize upon 

 the main source of the oxygen, viz. the oxyhsemoglobin, and so 

 obtain in wholesale quantity what the plasma can only supply in 

 retail*. This is effected, as we have seen, by the production of a 

 toxin which, doubtless by a process of haemolysis, breaks up the 

 red corpuscles into fragments and so liberates the contained 

 oxyhsemoglobin into the plasma, the rete ensuring that this 

 haemolysis and consequent solution of oxyhsemoglobin in the 

 plasma is effected in time for the dissolved pigment to be available 



* This reduction of the blood to the primitive invertebrate condition in which the 

 respiratory pigment is dissolved in the general plasma and not imprisoned in elastic 

 discs (the erythrocytes) as in Vertebrates raises the question as to why, if the former 

 condition enables the tissues to absorb the oxygen more readily, the latter condition 

 has arisen. Apart from a few lamellil)ranch and other Mollusca and a few Poly- 

 chajtes and PJioronis in which hasmatids have been described, all Invertebrates (and, 

 according to Lankester, also Amphioxus and the Leptocephalus larva of the Eel, hut 

 hajmatids have been stated to occur in the former and possibly exist in small number 

 in the latter) carry the respiratory pigment, when this is present (absent in the 

 tracheate. Arthropods, e. (C.), in the plasma, and it is difficult to understand what 

 advantage accrues from preventing the dissolved oxyhiBmoglobin coming into direct 

 contact with the tissues in vertebrate animals. It is of course possible that the 

 indirect distribution of oxygen by way of solution in the plasma conduces to a more 

 even and gradual supply to the tissues, especially in animals like Vertebrates in 

 which most of tlie tissues are very remote from the limited respiratory area of the 

 body surface ; in most Invertebrates, on the other hand, oxidation of the blood takes 

 place over most of the body surface and the tissues are all practically simultaneously 

 reached by the blood which, being contained in sinusoids rather than in capillaries, 

 bathes them on all sides. The more rapid circulation of the blood and larger 

 quantity of ha3moglobin in Vertebrates possibly compensate for the absence of 

 h;emoglol)in in the plasma. As is well known, when hff'inoglobin is liberated into 

 the plasma in Vertebrate blood, it is at once eliminated by the liver and kidneys. 

 See Addenda (2). 



