

NORMAL FORMATION OF MUCUS IN THE AIR-PASSAGES. 249 



and if, at the time of the experiment, the temperature of the living-room was 20 

 C., and the barometer-reading 750 mm., then the reduced volume of air corre- 

 sponding to the 4000 cu. cm. is V l = __^^J^_>^ = 3678 cu. cm., in which 



are contained 12.4 mgm. carbon dioxid. One mgm. of carbon dioxid, how- 

 ever, equals 0.508 cu. cm.; hence, there were in 3678 cu. cm. of air 6.299 cu. cm. 

 of carbon dioxid (12.4 X 0.508). In 1000 cu. cm. air this amounts to 1.7 cu. cm. 

 (according to the formula x : 1000 = 6.299 : 3678), or 1.7 of carbon dioxid in 1000. 



NORMAL SECRETION OF MUCUS IN THE AIR-PASSAGES. 

 THE EXPECTORATION (SPUTUM). 



The mucous membrane of the respiratory tract is covered by a thin 

 layer of mucus. This mechanically hinders further formation of mucus 

 by preventing the usual irritation of the air and dust. Additional 

 mucus is secreted only in so far as it is rendered necessary to replace 

 that lost by evaporation. As a rule, increased circulation of blood in 

 the tracheal mucous membrane is attended with increased secretion. 

 Division of the nerves on one side (in the cat) gives rise to redness on 

 the same side, with increased secretion. 



On "catching cold" (for instance, as a result of covering the abdomen with 

 ice) the mucous membrane first becomes completely pale, and then deep red, 

 with marked increase in the secretion. Injection of sodium carbonate and ammo- 

 nium chlorid restricts the secretion. The local application of alum, silver nitrate, 

 or tannic acid dries the mucous membrane, so that the epithelium is cast off. 

 Apomorphin, emetin, and pilocarpin actively stimulate the secretion; atropin and 

 morphin limit it. 



Even under normal conditions hawking and coughing will cause the 

 expectoration of slimy, viscid material, which may be derived from 

 the entire respiratory tract, and is always mixed with a little saliva. 

 In the presence of catarrhal conditions or of more serious disease the 

 expectoration becomes more profuse, and is often mixed with charac- 

 teristic products. It contains: 



1. Epithelial cells, especially squamous cells from the mouth and 

 the throat (Fig. 92, 8), more rarely alveolar epithelium (2), still more 

 rarely ciliated epithelium (7) from the larger air-passages. Not rarely 

 changes are found in the epithelium as a result of maceration, including 

 the cylindrical cells that have already lost their cilia (6) and contain 

 swollen nuclei. 



Alveolar epithelium (2), with a diameter from two to four times that of a 

 leukocyte, is found especially in the morning-sputum, but only in that from per- 

 sons over 30 years of age. In younger persons its presence indicates diseased 

 conditions of the pulmonary parenchyma. Alveolar epithelium is found also in 

 a state of fatty degeneration and filled with pigment-granules (3); also in the 

 form of myelin-degenerated cells (4), that is, cells filled with clear refractive 

 droplets of varying size, some being colorless, and some having absorbed pigment- 

 granules (dust-particles). Also mucin in myelin-forms, that is, in the form of 

 coagulated nerve-substance, is found constantly in the sputum (5). Mucus is 

 stained yellow by safranin, while albumin is stained red. 



2. Leukocytes (9) are present in large number in yellow sputum, 

 and in smaller number in clear sputum. They are to be looked upon 

 as white blood-corpuscles that have wandered from the blood-vessels. 

 They also are often found in changed forms and in a state of dissolution ; 

 they may be shrivelled up, filled with fat-granules, or they may appear 

 as conglomerations of granules; and, finally, isolated nuclei indicate 

 the destruction of their cell-body. 



