1904.J on Breathing, in Living Beings. 477 



be was one of the first to detect the presence of gases and CO^ in 

 blood. 



In story, one has beard of the " Quest of the Holy Grail." I have 

 even listened with rapt attention to an entrancing lecture on the 

 ^' Quest of the Ideal." For the cell, the quest is the " quest of 

 oxygen," and it is not happy till it gets it. 



We speak of a distinction between air-breathers and water- 

 breathers. If, however, we push the matter to its ultimate issue, we 

 find that all our tissues — and equally those of plants — live in a 

 watery medium; in us the fluid lymph which exudes from our 

 capillary blood-vessels, and in plants in the sap. Thus we come 

 upon what at first seems a paradox, but is not so ; all our cells not 

 only live in water, but they live in running water. They are bathed 

 everywhere by the lymph which is the 'real nutrient fluid for our 

 cells. Thus, in its final form, all respiration is actually aquatic. The 

 process of internal respiration, besides other conditions, requires the 

 presence of a certain amount of water. In fact, all vital phenomena 

 require the presence of water. 



The unity and identity of the process in animal and vegetable 

 cells, as the theatre of combustion, is the striking fact. The means by 

 which the necessary oxygen is brought to the cells is as varied as the 

 forms of animated organisms themselves. This function exists for 

 the cells, and not the cells for the function. 



If the mountain will not go to Mohammed, Mohammed must go 

 to the mountain. There are, at least, two principles on which animal 

 cells obtain oxygen. 



The air, or water containing air, is carried to the cells. This is 

 the principle adopted in the lower invertebrates, as in sponges and 

 with regard to certain air-breathers such as insects. 



The other principle is this, that an intermediary carries the 

 respiratory oxygen from some more or less central localised or diffuse 

 surface to the cells. This intermediary is the blood — an internal 

 medium of exchange. The fluid part of the blood may carry the 

 oxygen supply and remove the carbonic dioxide waste. This is the 

 case in many of the invertebrates, and it reaches its highest develop- 

 ment in the vertebrates. Hence in them the circulating and respira- 

 tory systems reach their fullest development. 



In most invertebrates the fluid part of the blood contains the 

 nutritive substances and also the oxygen and carbonic acid. In the 

 vertebrates, the haemoglobin of the red blood corpuscles carries the 

 oxygen from the gills or lungs to the tissues, whilst the CO2 is con- 

 tained in and carried chiefly by the blood plasma from the tissues to 

 the gills or lungs. 



It is singular that in the cephalopods, such as the squid and cuttle- 

 fish, the blood is bluish in tint ; and this is due to the presence in 

 the plasma of a respiratory pigment called haemocyanin. This body 

 has a composition like that of hsBmoglobin, but copper is substituted 

 for the iron of the haemoglobin. Copper also exists in organic 



2 K 2 



