10 THE MORPHOLOGY OF BACTERIA 



outer rim of the organisms, but it has now been established that these are not flagella 

 but bits of periplast torn off in fixation and staining. Under dark-field illumination no 

 refraction of light can be detected like that seen with the ciliated bacteria. The crista 

 present in some of the larger saprophytic spirochetes, the cristispiras, has been shown 

 to lack independent motility. Motility in the spirochetes must therefore be attributed 

 to streams of protoplasm passing through the bodies of the cells or to the presence of 

 contractile elements within, like the myonemes of certain protozoa. No definite dem- 

 onstration of myonemes has thus far been effected, although Noguchi has observed 

 bodies which strongly suggest them. Tt is possible that streams of protoplasm do exist 

 in these organisms and that their motility is due to changes of surface tension. A sat- 

 isfactory explanation of motility is very much needed. 



It is now generally admitted that the simpler spirochetes (treponema, spironema, 

 leptospira) multiply by transverse fission. It is true that appearances suggestive of 

 longitudinal fission have often been noted, but these were explained as the separation 

 of two organisms tightly coiled about each other. The chief evidence that spirochetes 

 divide transversely and not longitudinally depends upon accurate measurements of 

 the diameter of the cells, a method of study carried on especially by Shellack.' He as- 

 sumed that the diameter of the newly formed cells must at some time be one-half of 

 the diameter of the cells before division, if longitudinal division takes place. In careful 

 measurements of certain spirochetes {Spironema duttoni, novyi, etc.) Shellack was 

 never able to find organisms which were twice as thick as the thinnest forms. He was, 

 however, always able to find organisms twice as long as the shortest forms. He there- 

 fore concluded that the spirochetes always divide transversely and not longitudinally. 

 Lange" has recently called attention to the fundamental misconception in our inter- 

 pretation of measurements of all morphological types of bacteria. After equal binary 

 fission of spherical organisms the diameter of the daughter-cells is not one-half that of 

 the mother-cell, but equals the cube root of one-half the cube of the diameter of the 

 mother-cell, or over three-quarters of it. With cylindrical organisms the daughter- 

 cells are half as long as the mother-cells, after transverse division. After longitudinal 

 division the diameter of the daughter-cells equals the square root of one-half the 

 square of the diameter of the mother-cell, or a little less than three-quarters of it. 

 Since the spirochetes are practically cylindrical organisms, the failure to find organisms 

 whose diameter is one-half the diameter of the thickest cells cannot be regarded as ex- 

 cluding longitudinal division. 



A large number of spirochetes, especially the pathogenic varieties, show minute 

 spherical bodies in the interior of the cell, and these are occasionally extruded. These 

 bodies have frequently been regarded as reproductive elements. This conception we 

 owe primarily to Leishman who found numbers of granules in ticks infected with Spi- 

 rochaeta duttoni but no spiral organisms. With these ticks he was able to convey spi- 

 rochetal diseases experimentally. The matter was thoroughly investigated by Hindle^ 

 and by Balfour.-* Hindle, studying ticks infected with Spirochaeta gallinarum, found 



' Shellack, C: Arb. a. d. kais. Gesamle., 27, 364. 1908. 



"Lange, L. B.: J. Bad., 14, 275. 1927. 



J Hindle, E.: J. Parasitol., 4, 463. Cambridge, 1911. 



* Balfour, A.: /. Trap. Med., 10, 153. 1907; Brit. M.J., 2, 1130. 1907. 



