204 Notes, iii. 6. • 



"The lung, i^ all animals that have one, has a tendency to consist of two parts. But 

 the division is not so apparent in the vivipara as in the ovipara, and is least apparent in 

 man. But in the ovipara, that is in the birds and the oviparqus quadrupeds, the two 

 parts are so widely separate that there appear to be two lungs." As to the Ophidia, 

 where often only one lung is developed, he specially • mentions (ZT. A. ii. 17, 22) that their 

 lung is simple, i.e. undivided. 



2. Cf. ii. 16, Notes 10 and 11. It is noticeable that, though' A. considers the "innate 

 spirit " to be of a hot nature, he several times speaks of it as producing refrigeration ; not, 

 however, by its direct but by its indirect action, in causing fanning motions in the body. • 

 See iii. 6, Note 14. • 



3. A.*s theory of respiration, as expressed in the separate treatise on the subject, is as 

 follows. He rejects the opinion that the purpose of respiration is to keep up the internal 

 heat of the body {De Resp. 5, 6, and 4, 8), and holds that it has exactly the .contrary 

 object. Heat is being perpetually produced in the heart, and would accumulate in excess, 

 were there no means of reducing it when necessary {De Resp. 8, 6). The bloodless 

 animals produce so little heat, that no special arrangements are required to cool them ; 

 the simple bathing of their surface with air or water being sufficient as a rule for the 

 purpose {fie Resp. 9, i). Yet even in some of these, as in certain insects, there is a 

 provision, in the Hypozoma (ii. 16, Note 10), for the better reduction of the heat. In 

 sanguineous animals, however, that are of a hotter nature, there is always some special 

 provision for keeping the heat within bounds.- In fishes the reduction is effected by the. 

 water, which bathes the gills into which blood is conveyed from the heart {De Resp. 21, 6). 

 It is,, says A., the water itself and not, as some would have it, the air contained in the 

 water, which is the ageni of refrigeration. In support of this statement he urges several 

 arguments {De Resp, 3, 3), of which the chief is that no bubbles are given off by fishes 

 under water, as there would be were air inspired and expired. In other sanguineous 

 animals the internal heat is greater, and refrigeration is effected by the, more perfect 

 agency of air {De Resp.' 1% 2) inspired into a lung, air being a more perfect agent than 

 water because it cAn permeate the body mpre rapidly. The lung itself differs in different 

 animals, being more perfect the nobler, that is to say the hotter, the animal is. Thus it 

 is dry and bladder-like in ovipara (cf. Note 10) that are comparatively cool; and full 

 of blood in the vivipara that are of a hotter character {H. A. i. 17, 7.; De Resp. 3, 2). 

 The cold air, djawn into the lung, reaches the bronchial tubes (o-iJpcyyes), and as the 

 vessels containing hot blood run alongside these tubes and in immediate contact with 

 them {De Reip. 21, 4 ; II. A. iii. 3, 15), the air cools it, and carries off the Superfluous 

 heat ; as is shown by the fact that the air expired is much hotter than the air' inspired 

 {De Resp. 5, 6). Some of the air which enters the lun^ gets from the bronchial tubes 

 into the blood-vessels, although there is no direct communication between themj simply 

 owing to the close contiguity in which tubes and vessels lie (iii. 3, Note. 9). The air 

 permeates the body rapidly and cools the blood in the vessels, throughout the body, as 

 the air in the lung cools the greater heat in the heart. 



It appears then that lung and gills have the same function, and, says A., they conse- 

 quently never co-exist. No animal that has a lung ever has gills. "For it is best to 

 have a single organ for a single purpose ; and one method of refrigeration is enough for 

 any animal " {De Resp. 10, 6). As regards this last passage, we may remark that A. 

 was of course in complete ignorance of the perennibranchiate amphibia, so that^his. 

 erroneous statement that gills and lungs never co-exist may be passed over. • One cannot, 

 however, but ask, as did Galen, how he reconciles ^is present statement with his having 

 in fact attributed one and the ^ame function to lung and to brain. He nowhere explains 



