RESPIRATION 223 



one-fifth of the frequency of the ordinary respiratory move- 

 ments. The mere fixing of the attention on the observations 

 soon stopped the hiccup. 



Chemistry of Respiration. 



Our knowledge of this subject has been entirely acquired 

 in the last 200 years, and chiefly in the last century. 



Boyle showed by means of the air-pump that animals die 

 in a vacuum, and Bernouilli that fish cannot live in water 

 from which the air has been driven out by boiling. 



Mayow, of Oxford, seems to a considerable extent to have 

 anticipated Black, who in 1757 demonstrated the presence 

 of carbonic acid (carbon dioxide) in expired air by the 

 turbidity which it causes in lime-water. 



A most fundamental step was the discovery of oxygen by 

 Priestley in 1771, and his proof that the venous blood could 

 be made crimson, like arterial, by being shaken up with 

 oxygen. 



Lavoisier discovered the composition of carbonic acid, 

 and applied his discovery to the explanation of the respira- 

 tory processes in animals, the heat of which he showed to be 

 generated like that of a candle by the union of carbon and 

 oxygen. He made many further important experiments on 

 respiration, publishing some of his results in 1789, when the 

 French Revolution, in which he was to be one of the most 

 distinguished victims, was breaking out. He made the 

 mistake, however, of supposing that the oxidation of the 

 carbon takes place in the blood as it passes through the 

 lesser circulation. 



That some carbon dioxide is formed in the lungs there is 

 no reason to doubt, and the quantity may even be consider- 

 able (Bohr and Henriques). But that they are not the chief 

 seat of oxidation was sufficiently proved as soon as it was 

 known that the blood which comes to them from the right 

 heart is rich in carbon dioxide, while the blood which leaves 

 them through the pulmonary veins is comparatively poor. 



There are two main lines on which research has gone in 

 trying to solve the chemical problems of respiration : (i) 

 The analysis and comparison of the inspired and expired 



