RESPIRATION 161 



TABLE XXXIII 

 Composition of 



Inspired air. Expired Air. Alveolar Air. 



O 2 20-96 .. 16 .. 14-0 



CO 2 0-04 .. 4-4 .. 5-5 



N 2 . . 79-0 . . 79-6 . . 80-5 



Temp. . . Variable . . About 33-9 C.* . . 37-5 C. 



Moisture . . Variable . . Saturated at 33*9 C.* Saturated 



In this case expired air is approximately one. part of inspired 

 air (from dead space) and two parts of alveolar air (170 c.c. 

 from dead space and 330 c.c. from alveoli = 500 c.c.). 



To study the chemical changes of respiration we need to 

 bear the above facts in mind. If we wish to study the total 

 oxidation in the body we must measure the total volume of 

 air respired and the changes in its composition, but if we 

 wish to study the exchange of gases between the blood and 

 the alveolar air it is the composition of alveolar air that is 

 required. 



TRANSPORT OF GASES 



Respiratory Pigments. When the activity of cells becomes 

 greater than a certain value a current of water cannot supply 

 enough oxygen. In order to overcome this difficulty respira- 

 tory pigments are used. These pigments can serve two 

 purposes : first, as local deposits, which can accumulate a 

 supply of oxygen to be used up during periods of activity ; and 

 secondly, as part of the circulatory mechanism to convey 

 oxygen from the gills or lungs to the tissues. The colours 

 of anemones, etc., have been stated to be storehouses of 

 oxygen.f 



There are two main respiratory pigments. One, haemo- 

 cyanin, a copper-containing compound which is colourless 

 when deprived of oxygen and becomes slightly bluish when 

 brought into contact with the oxygen of the atmosphere. { 

 This pigment is confined to some invertebrates and is much 

 less efficient than the other pigment. 



The second pigment, haemoglobin, is one containing iron, 

 and it is found in the circulating blood of vertebrates ; it 

 also occurs in isolated situations in the invertebrate phyla. 

 We shall proceed to a consideration of the behaviour of this 

 pigment. 



* W. A. Osborne, Journ. Physiol., 1913, vol. 47, Proc. p. xii. 

 f F. W. Gamble, Animal Life. Murray, 1908, p. 108. 

 \ L. Fredericq, Arch, de Zool. exper., 1878, vol. 7, p. 535. 

 11 



