8o RESPIRATORY EXCHANGE OF ANIMALS AND MAN 



the haemerythrin of its blood changed colour to oxyhaemerythrin when 

 the animal was brought into oxygen-rich water. 



On fresh- water fishes Winterstein [1908] has made a number of 

 determinations showing that the oxygen consumption is practically 

 independent of the oxygen pressure down to about 2 per cent, pressure 

 (07 c.c. O. 2 per litre). 1 



Thunberg [1905] has made a number of very careful experiments 

 on certain air-breathing animals : Lumbricus, Limax, Tenebrio larvae. 

 The results are summarized in the following table of averages. The 

 gas exchange of the animals in air is taken as 100. The single ex- 

 periments agree on the whole extremely well with one another. 



TABLE IX. 



The results obtained on the meal-worm (Tenebrio) and oi> Limax 

 are shown graphically in fig. 21. 



Thunberg assumed that the oxygen tensions in the tissues were 

 proportional to and only slightly lower than in the surrounding air, and 

 considered the results as showing the mass action of the oxygen in 

 the oxidative reaction. As the respiration mechanisms of these 

 animals are rather imperfect, 2 however, it is perhaps more probable to 

 assume that the oxygen tension in large parts of the tissues has in all 

 cases been very nearly zero. This assumption will at all events bring 

 Thunberg's results into line with those of Henze and Winterstein, and 

 it would seem to be a more or less general rule for cold-blooded 



1 It should be borne in mind in this connection that at low temperatures and with a 

 low CO 2 pressure the dissociation curve of oxyhaemoglobin rises very rapidly and that practi- 

 cally complete saturation may be reached at a very low pressure. 



2 The meal-worm is a tracheate insect but has not been observed to make respiratory 

 movements. The earth-worm has no special respiratory organ. 



