MORPHOLOGY 583 



oval, and slightly pointed at the ends (hence the comparison with grains of 

 barley or a candle flame and the synonym Diplococcus lanceolatus) . Two 

 cocci are generally joined together with their long axes in the same 

 straight line, like a figure of 8 forming a diplococcus, but here and there a 

 few single cocci may be found, and sometimes short chains composed of 

 three or four cocci. The organisms whether occurring as single cocp.i, diplo- 

 cocci or in chains are surrounded by a capsule 

 or areola, which is a sort of albuminous en- S."^ 

 velope : this capsule can be stained by appro- * 9 



priate methods. % 



The pneumococcus varies considerably in size : % % 

 0-5orO'75/xtolorl-25/*. * 



Staining reactions. The pneumococcus is 4jSa- * 

 readily stained with the basic aniline dyes and $KJs 

 is gram-positive. The following methods are ^ 



recommended for diagnostic purposes. jf ^ **'>.<, 



(a) Nicolle's method. Recommended. Films 

 prepared in the ordinary way are stained with 

 carbol-thionin for some seconds then passed 



i i A i TIT.! /-i j_ o\ i i FIG. 27o. Pneumococcus. x 1000. 



quickly through alcohol-acetone (1 to 3), washed, stained to show capsules, 



dried and mounted. 



(6) Gram's method. Gram's method should always be used in the identifi- 

 cation of the pneumococcus ; blood-films give very pretty preparations. 

 The double staining method recommended on p. 207 should be adopted. The 

 capsules, as a rule, remain unstained. 



(c) Capsule staining. The method (a) recommended above for staining 

 the pneumococcus will stain the capsules : several other methods of capsule 

 staining applicable to the pneumococcus have already been described in the 

 earlier part of the book (p. 147). 



*-'* v 1 " 9 ^ 



4 ; \V$j ; 



* tjw > % **$ ; : ^ 



^ ^V ' - ^ "' 



* ** ' : '^*r : ^ Sg< ^c ^ "s 



FIG. 276. Pnenmoc.occus. Section of lung. Gram's stain and eosin. 

 (Oc. 2, obj. T Uh, Zeiss.) 



(d) Section staining. (i) Sections are best stained by Gram's double or 

 triple stain (p. 219). Weigert's method may also be used (p. 216). 



(ii) It is a somewhat difficult matter to stain capsules in sections : one or 

 other of the following methods may be tried. 



