184 Chapter XII 



out of the domain of vasomotor effects in the two lungs by control 

 experiments on atropinised lungs. 



The experiments carried out by Maar on the tortoise were, to 

 some extent, supported by those of Spallitta, an Italian physiologist, 

 on the turtle. This author found that whatever mixture of gas was 

 put into the turtle's lung, and enclosed therein, the oxygen was 

 practically all absorbed, whilst the C0 2 was always found to be 

 about 6-5%. 



Xor was the action of the vagus on the respiration of warm- 

 blooded animals overlooked in the Copenhagen laboratory. Henriques 

 studied the effect of brief stimulation of the vagus on the gas exchange 

 of dogs. Practically it resembled that of the tortoise, namely, it 

 inhibited the secretion of oxygen relative to CO 2 , and in this way 

 caused the respiratory quotient to approach unity. Here again 

 circulatory changes were supposed to have been excluded since the 

 change in the respiratory quotient was produced in cases in which 

 the circulation was both quickened and slowed. 



We are not now criticising the case for secretion in the lung but 

 merely stating it, and from the statement it appears that right up 

 the animal kingdom there is evidence, which sometimes appears good 

 and sometimes bad, for the possibility of active secretion of gas, the 

 activity being influenced, sometimes in one way, sometimes in another, 

 by the nervous system. 



The diffusion and the secretory theories were then rivals. The 

 one is simple, inasmuch as it demanded of the lung no greater 

 powers than are possessed by a piece of parchment, but it involved 

 no great biological generalisation ; it is a theory which attracts the 

 physicist because it presents a simple and intelligible relation of facts 

 as they are, but which repels the biologist because his training has 

 taught him to regard the different organs of the body as specialised 

 groups of cells which confine their activity to carrying out individual 

 fractions of the functional complex appertaining to living protoplasm. 

 The other theory may be said to be complicated, but at least it 

 demands no greater mystery than is conceded to almost every other 

 cell of the alimentary tract the mystery of metabolic activity on the 

 part of the cell itself. This may be among the greatest of all mysteries, 

 but it may fairly be claimed that an even greater would be a cell 

 whose purpose was in no way a reflection of its own metabolic 

 activity. 



Nor must the reader in judging the theory of pulmonary secretion 



