RESPIRATION. 605 



in a satisfactory manner by Malpighi, in his two epistles De Pal- 

 mombus, first published in 1661. He showed that the interior 

 portion of the lungs was composed of lobules, in the intervals 

 between which were numerous vesicles communicating with each 

 other, and with the branches into which the trachea is divided, 

 and consequently always filled with air. These vesicles are lin- 

 ed with blood-vessels, which expose the blood from the right 

 ventricle of the heart to the action of the air. This structure of 

 the lungs was confirmed by the subsequent dissections of Tho- 

 mas Bartholin ; though he had previously held a contrary opi- 

 nion. 



After the structure of the lungs was ascertained, some time 

 elapsed before anatomists were agreed about the mechanism of 

 respiration. Swammerdam, in 1667, adopted the opinion of 

 Des Cartes, according to whom the air is forced into the lungs 

 by the increased density of the air around the breast, occasioned 

 by the dilatations of the thorax, in consequence of the elevation 

 of the ribs. This absurd theory seems to have been first refut- 

 ed by Dr Walter Needham, in his celebrated work De Formato 

 Fcetu, published in 1667. In 1674, it was examined and opposed 

 at greater length by Dr Lamzweerde, a physician in Cologne. 

 The true mechanism of respiration, the elevation of the ribs, and 

 the action of the intercostal muscles * were pointed out. It was 

 shown that, by the elevation of the ribs, and the depression of 

 the diaphragm, a partial vacuum is produced in the thorax. This 

 causes the air to be forced into the vesicles of the lungs. That 

 organ, of consequence, is pressed against the walls of the thorax, 

 and its cells at every inspiration are filled with air. 



It has been already stated, that the almost universal opinion 

 of physiologists was, that the use of the lungs was to cool the 

 blood. The chyle was supposed to be converted into blood in 

 the liver. One of the first steps towards explaining the nature 

 of respiration was made by Dr Hooke, in his Micrographia, pub- 

 lished in 1665. He gives a theory of combustion in that work, 

 which applies very closely to the opinions entertained on the sub- 

 ject by modern chemists. The air, according to him, contains 

 a small quantity of a peculiar matter, identical with a substance 

 which exists in nitre. This substance has the property of rapid- 

 ly dissolving combustibles, and the phenomena of combustion are 



* De Respiratione, p. 278. 



