272 ■ THE LUNGS. 



of dark slate-colour, which sometimes increase to such a degree as to 

 render the surface almost uniformly black. 



The dark colom-ing- matter found in these streaks is in the form of granules and 

 collections of granules, frequently not inclosed in cells ; it is dei^osited in the in- 

 terstitial areolar tissue mostly near the sui'face of the lung, and is not found so 

 abundantly in the deeper substance. It exists sometimes in the air-cells, and on 

 the coats of the larger vessels. Its qviantity increases with age, and is said to be 

 less abundant in females than in males. In persons wlio follow the occupation of 

 miners, more especially colliers, the lungs are often intensely charged with black 

 matter. The black substance seems mainly to consist of particles of carbonaceous 

 substance. It is found also in the bronchial glands ; indeed, it appears to be 

 taken u]i in large measure by the lymi^hatics. In exceptional cases the adult 

 lungs exhibit only vciy slight streaks of pigment. 



Condition in the foetus and changes after birth. — In the fcotus the lungs 

 contain no aii', and consequently sink in water. 



For a long time tlie lungs are very small, and occupy only a limited space at 

 the back part of the chest. In an embryo, 16 lines in length, their proportionate 

 weight to the body was found by Meckel to be 1 to 25 ; in another, 29 lines long, 

 it was 1 to 27 ; in another 4 inches in length, 1 to 41 ; and at the full period, 1 

 to 70. Huschke found that the lungs of stiU-born male childi-en were heavier in 

 proportion to the weight of the body than those of female children ; the ratio 

 being, amongst females, 1 to 76, and in males, 1 to do. 



The lungs undergo very rapid and remarkable changes after birth, in conse- 

 quence of the commencement of respii'ation : these affect theii' size, position, 

 form, consistence, texture, colour', and weight, and should be carefully studied, 

 as furnishing the only means of distinguishing between a still-born child and 

 one that has respired. 



1. Foiiltlon, size, ami form. — In a foetus at the full period, or in a still-born 

 child, the lungs, comparatively small, lie packed at the back of the thorax, and 

 do not entirely cover the sides of the pericardium ; subsequently to respiration, 

 they expand, and completely cover the plem-al portions of that sac, and are also 

 in contact with almost the whole extent of the thoracic wall, where it is covered 

 with the pleiu'al membrane. At the same time, tlieir previously thin sharp margins 

 become more obtuse, and theii" whole form is less compressed. 



2. Coti.t'hstcnve, frxturc, and colotir. — The introduction of air and of an increased 

 quantity of blood into the foetal lungs, which ensues immediately iipon bii-th, 

 converts their tissue from a compact, heavy, granirlar, yellowish-i^ink, gland-like 

 substance, into a loose, light, rose-pink, spongy structiu-e, which, as already men- 

 tioned, floats in water. The changes thus simultaneously produced in their 

 consistence, colour, and textui'e, occiu' first at their anterior borders, and iDroceed 

 backwards through the lungs : they, moreover, ajjpear in the right lung a little 

 sooner than in the left. 



.3. Wciiiht. — The ab.whitc )reif/ht of the lungs having gi-adually increased from 

 the earliest period of develoj^ment to ))irth, undergoes at that time, from the 

 quantity of blood then poured into them, a very marked addition, amounting to 

 more than one thiixl of their previous weight : for example, the lungs before 

 bii'th weigh about one and a half ounce, but, after complete expansion by respi- 

 ration, they weigh as much as two and a half ounces. The rcla-tive nrif/Jit of the 

 lungs to the body, which at the termination of intra-uterine life is about 1 to 70. 

 becomes, after respiration, on an average, about 1 to 35 or 40 ; a proportion 

 which is not materially altered through life. The specific gravity is at the same 

 tune changed from 1'056 to about •342. 



4. Cltange.^ hi the trachea after hirth. — In the fojtus the trachea is flattened 

 before and liehind, its anterior sui-face being even some'U'hat depressed ; the ends 

 of the cartilages touch ; and the sides of the tube, which now contains only 

 mucus, are applied to one another. The effect of respiration is at first to render 

 the trachea open, but it still remains somewhat flattened in front, and only later 

 becomes convex. 



