GLANDS. 91 



inch, or more. In the adult, as a rule, the outline of 

 the bases of these lobules is marked on the surface of 

 the lung by a variable amount of black pigmentary 

 deposit, 



from the tip of each terminal bronchial twig. The sacs connected with 

 one "bronchial termination do not communicate with those of another ; 

 each set of air-sacs is therefore a little lobule, or lobulette, which, in fact, 

 represents the entire arrangement of the lung, and is a lung in miniature." 

 (The resemblance of a lobulette to the entire lung of a frog, is elsewhere 

 strongly emphasized.) " As the air-nacs pass towards the boundary of 

 the lobulette, they often bifurcate, and here and there circular orifices 

 exist, which lead to smaller sacs, sometimes only to a small group of air- 

 cells or alveoli, so small as scarcely to be considered a sac." The author 

 adopts the term alveolus from Rossignol as preferable to air-cell, or air- 

 vesicle, both of which he considers objectionable. " A pulmonary alve- 

 olus is that portion of an air-sac which exists in its wall, and is circum- 

 scribed by a slightly raised margin, consisting of thin membrane, and 

 constituting a cup-like depression. In shape it is more or less polygonal. 

 The alveoli are found throughout the circumference of the sacs, and at 

 their fundus, varying in number in each sac from eight to twenty.'" 1 

 u If we trace the sacs from their fundus we may say that, passing from 

 the periphery of the lobulette, and diminishing somewhat in size, they all 

 terminate in the dilated extremity of the bronchial tube," by the common 

 orifice already described. " The sac?, as they pass in this manner, often 

 join, two and three together, and others terminate in a single mouth." 

 . . . . " The tube which results from the union of two sacs has a 

 smaller capacity than that of the two sacs taken together, but a larger 

 capacity than either of them individually." .... "The shape of 

 these groups of air-sacs, or lobulettes, is more or less pyriform, the apex 

 being situated at the termination of the bronchial tube ; the base, 

 somewhat flattened, especially at the superficies of the lung, at the distal 

 extremity of the sacs. A most excellent way of examining the air-sacs^ 

 and one which demonstrates most satisfactorily the manner in which those 

 at the surface of the lungs are arranged with reference to the bronchial 

 tubes, is the following : a thin slice should be cut off the surface of a 

 portion of lung which has beerr injected, inflated, and dried, and the 

 portion itself (not the slice) should then be placed under the dissecting 

 microscope. The cut orifices of the air-sacs will be observed. Very 

 fine bristles should then be inserted into these tubes, the largest one being 

 first chosen. It will be found that several of the bristles, passing into 



