THE SPUTUM l6l 



portance of securing material directly from the lungs has been 

 explained. 



Where it is necessary to work with material which has been 

 collected without any precaution, the microscopical nature of 

 the cells may afford a clue as to its origin. Mucus or muco- 

 pus derived from the mouth, pharynx, etc., is characterized by 

 containing squamous cells; these are of large size, flattened, 

 have a comparatively small nucleus, and are often collected 

 into groups of three or four, with a distinct tessellated ar- 

 rangement. They contain granules (of keratin or an allied 

 substance) which stain deeply by Gram's method; they are 

 also the last substances (other than acid-fast bacilli) to be 

 decolorized by the acid in the Ziehl-Neelsen process, and when 

 the decolorization has not been carried out quite completely, 

 may remain stained in the form of pinkish plaques. The sputum 

 which comes from the bronchi may be characterized by the 

 presence of columnar cells, which are occasionally found to 

 be ciliated, but in most cases this sign fails, and the sputum 

 consists of mucus enclosing polynuclear leucocytes and no 

 characteristic cells of any kind. The same is true of the 

 sputum from the lungs; there is frequently nothing to dis- 

 tinguish it from that of other regions, and this is especially 

 the case when it is derived from a cavity which is lined with 

 pyogenic membrane. But sometimes the sputum contains 

 very characteristic alveolar epithelial cells. These are derived 

 from the lining* of the alveoli, the cells of which lose their 

 flattened shape and become spherical in many pathological 

 conditions. They are large round or oval cells, much larger 

 than the polynuclear leucocytes, and have clear protoplasm 

 and a round or oval nucleus, which is often placed eccentrically. 

 They are actively phagocytic, and their contents give an im- 

 portant clue to the nature of the pathological process at work 

 in the lung's, since they are derived directly from the alveoli. In 

 pneumonia they may be seen to contain pneumococci, and this 

 is especially the case after the crisis; in congestion, and es- 

 pecially passive congestion, of the lung they are packed with 

 red corpuscles, often in various stages of destruction, or with 

 granules or crystals of altered blood-pigment. In diseases 

 due to dust the cells contain fragments of the dust in ques- 

 tion, but it must be remembered that particles of coal-dust are 

 often found in them in normal conditions in city dwellers. 



ii 



