MORPHOLOGY, REPRODUCTION, ETC. 21 



tures may contain long, irregularly beaded forms with broad expan- 

 sions at the ends. In the case of B. pestis the fact that large numbers 

 of oval, vacuolated bodies in old cultures are formed regularly has 

 become of differential value. 22 These degeneration forms are shown 

 most characteristically when the bacteria are cultivated on agar 

 containing 3 to 5 per cent NaCl. 



Among the cocci, marked evidences of involution are often seen 

 in cultures of the meningococcus in the form of large, swollen poorly- 

 staining spheres, and in the case of the pneumococcus in the so-called 

 shadow forms which have the appearance of empty capsules. There 



FIG. 7. DEGENERATION FORMS OF BACILLUS PESTIS. (After Zettnow.) 



are few microorganisms indeed, in which prolonged cultivation on 

 artificial media or other unfavorable influences do not produce varia- 

 tions from the ground type which may often make the cultures mor- 

 phologically unrecognizable. In the case of many of the spirilla 

 (spirillum Milleri, spirillum Metchnikovi, etc.) the degeneration 

 forms may appear within so short a time as two or three days after 

 transplantation. 



CHEMICAL CONSTITUENTS. The bacterial cell has been found to 

 contain proteins, nucleic acid, carbohydrates, fatty substances and 

 ash. The quantitative chemical composition of dried mass cultures 

 of bacteria, even of the same species, shows rather extreme varia- 



22 Hanlcin and Leumann, Cent, f . Bakt., I, xxii, 1897. 



