370 DISCOVERY REPORTS 



as possible at each opportunity, to get rid of all the carbon dioxide excreted from the 

 blood and take in air containing its full complement of oxygen. 



The histological structure of the whale's lungs has been examined in search of any 

 adaptations to the whale's peculiar mode of life. Photomicrographs of distal portions 

 of lungs stained to show elastic tissue and cartilage are shown in Plate XV. Lungs of 

 two species of southern whale are shown : Humpback and Fin whale, each magnified 540 

 times. The main features of these lung sections are the great thickness of the walls of 

 the infundibula and alveoli compared to those of a man or pig, and the presence of thick 

 bands of elastic tissue surrounding each infundibulum. The epithelial cells of the in- 

 fundibula seem to be embedded in a mass of spongy material. The Fin whale lung 

 (PI. XV, fig. 2) is quite collapsed, so that many infundibula are almost invisible. The 

 Humpback lung (PI. XV, fig. i) was full of water some time before the dissection was 

 begun, and this may account for the smaller degree of collapse which seems to have 

 occurred. The presence of such large amounts of elastic tissue in the infundibula probably 

 enables the lung to collapse readily and completely when the whale expires, so that the 

 only air left in the lungs is that in the "dead space", or non-flexible portions of the 

 lungs, such as the trachea and bronchi. 



Inspiration and expiration. There is further reason to suppose that the whale 

 makes a more complete change of air in the lungs on each occasion than any other 

 mammal. The blast of expiration, which in the Antarctic is clearly visible as a column of 

 condensing vapour, is usually seen to rise to a height of 20 ft. in half a second ; the noise 

 of the expiration is audible on a still day for a distance of at least half a mile. It is 

 obvious that expiration is extremely forcible and that a vast volume of air passes through 

 the blowhole with great velocity. 



I have been able to time the acts of expiration and inspiration on occasions when the 

 whale was so close that the movements of the blowhole could be seen. Sometimes it 

 was possible to distinguish the sound of expiration and the more subdued sound of air 

 rushing into the lungs. Otherwise the time of inspiration was taken to be the interval 

 between cessation of the blast and the closing of the blowhole, allowance being made 

 for sound lag due to distance. The total time taken from the commencement of the 

 expiratory blast to the closing of the blowhole preparatory to submersion averages 

 I -5 sec. Expiration lasts o-6 sec. ; inspiration takes longer, 0-9 sec. Bennett (1931), from 

 personal observation, estimates 2 sec. for the complete act. No attempt seems to be 

 made by the whale to start expiration before the surface of the sea has been broken. 

 A Blue whale may breathe twice in succession with an interval of about i min. after a 

 long dive, but normally only one breath is taken at a time. 



HYDROSTATIC PRESSURE 



As has been indicated above whales are accustomed to undergo considerable pressure 

 in the course of submersion. For every 10 m. depth the pressure is increased by i atmo- 

 sphere, or 14 lb. to the sq. in., so that the absolute pressure bearing on the surface of a 

 whale is 14 lb. per sq. in. plus another 14 lb. per sq. in. for every 10 m. submersion. 



