4 DISCOVERY REPORTS 



The lungs are massive, those of a large Blue whale weighing over a ton (Laurie, 1933, 

 p. 404). This weight includes an unknown quantity of blood, but since the lungs were in 

 a collapsed state it is thought that the amount of blood remaining in them was small. 

 It is not practicable to ligature the trachea of a whale before removing the lung, so that 

 all the specimens examined are perforce from collapsed lungs. The degree of collapse is 

 considerable, as is to be expected from the quantity of elastic tissue present both in the 

 pleura and in the lung substance. 



The size and weight of whale lungs render anatomical investigation practically 

 impossible, since the difficulties of injecting the vascular system would be immense. We 

 must therefore be content with the foregoing facts and with the observation that the 

 collapsed lung when cut with a knife resembles in texture and appearance a rubber 

 sponge permeated with blood. 



Structure of alveoli. These ultimate subdivisions of the bronchioles are the subject 

 of our histological study. In land mammals the air spaces of the alveoli are separated 

 from one another by thin septa consisting of a layer of epithelium bounding each air 

 space, with a capillary network in between. When the alveoli are expanded, as after 

 inspiration, the septa are virtually five cells thick and are composed in cross-section of 

 epithelium, capillary endothelium, blood cells flowing in single file, capillary endo- 

 thelium again, and epithelium. In the collapsed lung the situation is essentially the 

 same, allowing for some overlap of the cells of epithelium and capillary endothelium. 

 The whole structure is a means of exposing blood to the respiratory gases in the most 

 efficient manner, since rapid diffusion from the gases to the blood and vice versa can 

 take place in two directions at once. 



In cetacean lungs, on the contrary, a different arrangement is found. The septa are 

 very thick, being largely composed of collagen of indeterminate structure and corre- 

 spondingly difficult to portray. The collagen is heavily invested with long strands of 

 connective tissue and is sparsely nucleated. Owing to the thickness of the septa a single 

 capillary network cannot serve for two adjacent alveoli, and instead each air space is 

 bounded by a separate capillar}- network. The most important feature is the complete 

 absence of epithelium. The membrane which separates the blood from the air spaces is 

 very thin capillary endothelium. Occasional nuclei are to be seen adjacent to the air 

 space; their shape is that of endothelial nuclei. In Plate I, fig. 7, a high magnification 

 drawing of a section of lung from a Southern Right whale, the capillary can be seen 

 leaving an arteriole running in the interalveolar stroma. The close network of capillaries 

 surrounding the air spaces is seen to contain red blood corpuscles, though owing to the 

 collapsed state of the specimens and the inevitable post-mortem haemorrhage the 

 capillaries are not altogether filled with blood. 



The lack of alveolar epithelium and the exposure of the capillary network to the 

 respiratory gases is believed to be unknown hitherto in the lungs of those land mammals 

 which have been examined. In these latter epithelium is always found. [The lungs of 

 birds are reported to lack epithelial lining (Hartridge, 1936, p. 203).] 



