278 HISTORICAL. 



Amongst the lower invertebrata some breathe by gills, others by means of a special 

 " water-vascular system," and others again by no special organs. 



Aristotle (384 B.C.) regarded the object of respiration to be the cooling of the 

 body, so as to moderate the internal warmth. He observed correctly that the 

 warmest animals breathe most actively, but in interpreting the fact he reversed 

 the cause and effect. Galen (131-203 A.D.), thought that the " soot" was removed 

 from the body along with the expired water. The most important experiments on 

 the mechanics of respiration date from Galen ; he observed that the lungs passively 

 follow the movements of the chest; that the diaphragm is the most important 

 muscle of inspiration; that the external intercostals are inspiratory; and the internal, 

 expiratory. He divided the intercostal nerves and muscles, and observed that 

 loss of voice occurred. On dividing the spinal cord higher and higher, he found 

 that as he did so, the muscles of the thorax lying higher up, became paralysed. 

 Oribasius (360 A. D.) observed that hi double pneumothorax both lungs collapsed. 

 Vesalius (1540) first described artificial respiration, as a means of restoring the 

 beat of the heart. Malpighi (1661) described the structure of the lungs. J. A. 

 Borelli (f 1679) gave the first fundamental description of the mechanism of the 

 respiratory movements. The chemical processes of respiration could only be known 

 after the discovery of the individual gases therein concerned. Van Helmont 

 (t 1644) detected C0 2 . [Joseph Black (1757) discovered, by the following experi- 

 ment, that C0 2 or "fixed air" is given out during expiration: take two jars of 

 lime water, breathe into one through a bent glass tube, and force ordinary air 

 through the other, when a white precipitate of calcium carbonate will be found to 

 occur in the former.] In 1774 Priestley discovered O. Lavoisier detected N (1775), 

 and ascertained the composition of atmospheric air, and he regarded the formation 

 of C0 2 and H 2 of the breath as a result of a combustion within the lungs 

 themselves. J. Ingen-Houss (1730-1790) discovered the respiration of plants. 

 Vogel and others proved the existence of COg in venous blood, and Hoffmann and 

 others that of in arterial blood. The more complete conception of the exchange 

 of gases was, however, only possible after Magnus had extracted and analysed 

 the gases of arterial and venous blood (p. 55). 



