114 CLINICAL BACtERIOLOGY AND HEMATOLOGY 



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 compara- 

 tively small nucleus, and are often collected into groups of three 

 or four, with a distinct tessellated arrangement. 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 occa- 

 sionally 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 charac- 

 teristic 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 important clue to the nature of the patho- 

 logical process at work in the lungs, 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 especially 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 question, 

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

 found in them in normal conditions in city dwellers. 



In asthma the characteristic Curschmann's spirals may be seen, 

 and the cells will be found to consist almost entirely of eosinophile 

 leucocytes. 



