Dienes: PPLO & Bacterial L Forms 377 



processes of the organisms are very simple. The basic elements are small gran- 

 ules between 0.15 and 0.3 ^ in diameter that multiply by fission after elonga- 

 tion. Somewhat larger forms may divide by extruding short filaments. In 

 addition the granules may form more or less large aggregates enclosed in a 

 common envelope out of which they again grow. The structure of such large 

 bodies is essentially similar in cultures of bacteria, L forms, and PPLO. In 

 the organisms of bovine pleuropneumonia, and possibly in a few other strains, 

 the granules also can grow into thin filaments. This form of growth was not 

 observed in most strains. 



L forms, like PPLO, do not have rigid cell walls. This lack of a rigid cell 

 wall is demonstrated in thin sections of L forms examined with the electron 

 microscope. Chemical studies indicate that the L forms do not have the 

 chemical complexes that are responsible for the rigidity of bacterial cell walls. 

 A large part of the similarity of L forms to PPLO is the consequence of this 

 lack. However, some of the similarities to PPLO do not seem to be the im- 

 mediate consequence of the absence of a rigid cell wall. One of these is the 

 small size of both PPLO and the L forms. According to filtration measure- 

 ments by Klieneberger, the size of viable granules in the L forms of Streptoba- 

 cillus moniliformis is similar to, or only slightly larger than, the size of PPLO. 

 The electron microscope shows granules of similar size in both groups. An- 

 other property not directly connected with the cell wall, common to both 

 groups, is the tendency of the growing organisms to embed themselves in agar. 

 Multiplication in agar cultures occurs mainly inside the agar. The charac- 

 teristic appearance of the colonies in both groups is the consequence of this 

 tendency. Both groups of organisms invade agar only and not other solid 

 media. Finally, a remarkable property of both groups is the tendency to grow 

 into large bodies. This tendency is greater in the L forms than in PPLO. 

 The L forms in broth or in gelatin multiply only by the growth of granules to 

 large bodies and by the liberation of granules from the large bodies. 



As noted above, bacteria also tend to grow into large bodies. Transforma- 

 tion of bacteria to L forms is always preceded by the appearance of large 

 bodies, and the L forms grow out of the large bodies. In a few instances 

 large bodies were observed during forniation from bacteria,** and like bac- 

 terial filaments, these bodies developed by multiplication without separation 

 of the bacteria. In the early stages large bodies disintegrated into a group 

 of bacteria by the development of cell walls between the constituent organisms. 

 After this period, the large bodies reproduced bacteria for a certain length of 

 time. Later, an increasing number lost the ability to develop or they pro- 

 duced L forms. Some of the L forms so produced, like the large bodies de- 

 veloping from bacteria, return immediately to bacterial form when the influ- 

 ence resulting in these transformations, e.g., penicillin, is eliminated. Most L 

 forms revert to a bacterial form of growth only occasionally and after long 

 cultivation may lose this ability completely. 



The large bodies are formed in these instances, under conditions which in- 

 hibit the multiplication of the single organisms, by multiplication of organisms 

 possessing the full potentialities of bacteria. After some time the abihty to 

 return to bacteria is lost, but the organisms are able on agar media to multiply 



