THE ORGANISM OF PLEUROPNEUMONIA 



941 



centre surrounded by a smooth transparent peripheral extension (Fig. 223). Well- 

 developed colonies may reach a diameter of 2 mm. Cultivation is also successful 

 on the chorio-allantoic membrane of the developing chick embryo (Tang et at. 1936). 

 Swift (1941), however, found that both the organism of pleuropneumonia itself 

 and seven other strains of the same group grew better on dead membranes, prepared 

 by freezing the embryo for an hour with dry ice, than on living membranes — a 

 point of possibly some differential importance from Rickettsia and the filtrable 

 viruses. On living membranes no constant macroscopic lesions were produced, 

 and the embryo was not killed. 



Morphology. — The morphology of the organism is influenced by a number of 

 factors, particularly the age of the culture and the method of examination. Growth 

 of organisms of the pleuropneumonia group appears to be accompanied by the 



Fio. 224. — Organism of 

 Pleuropneumonia. 



Elementary bodies, granules, 

 or conidioids. Dark-ground 

 illumination (x 3600). 

 (After Turner.) 



D 



Fig. 223. — Organism of 

 Pleuropneumonia. 



Surface colonies on serum 

 agar ( x 140). 



(After Tang et al.) 



Fig. 225. — Organism of 

 Pleuropneumonia. 



Spheroid showing unipolar 

 germination. Dark-ground 

 illumination (x 3600). 

 (After Turner.) 



Fig. 226 (Inset). — Organism of 



Pleuropneumonia. 

 Spheroid showing multipolar ger- 

 mination. Dark-ground illu- 

 mination ( X 3000). 



(After Turner.) 



Fig. 227. — Organism of 

 Pleuropneumonia. 

 Multipolar germination, showing 

 how the buds have moved away 

 from the parent spheroid and 

 are developing into filaments. 

 Dark-ground illumination ( X 

 3600). (After Turner.) 



formation of large amounts of cholesterol and cholesterol esters from the serum 

 in the medium (Partridge and Klieneberger 1941). These bodies are present as 

 the myelm forms of lecithin, and assume the most bizarre shapes (Williams 1941). 

 In addition, there is reason to believe that the protoplasm of the organism itself 

 is m some stages of its development peculiarly plastic, and is readily distorted 

 by external pressure or tension. Since many workers have used different methods 

 of examining cultures, and since most of these methods have entailed a risk of 

 distortmg the microbial elements, it is not surprising that the observations recorded 

 have often been diverse, conflicting, and difficult to interpret. More recently 

 Kheneberger and Smiles (1942) and Klieneberger (1942) have described methods 

 for exammmg cultures in situ, either by reflected light on a dark ground using 

 annular oblique incident illumination, or by fixation and staining. The use of 

 these methods suggests that the developmental process of the pleuropneumonia 

 group of organisms is simpler than had formerly been believed, and that the 



