CHAPTER I 

 THE NEWER KNOWLEDGE OF THE MORPHOLOGY OF BACTERIA 



HERBERT C. WARD 



School of Hygiene and Public Health, Johns Hopkins University 



For years bacteriology, dominated by the cellular doctrine of Virchow, has ac- 

 cepted the thesis, more or less completely proved by Cohn and Koch, that each bacte- 

 rial cell is derived from a previously existing cell of practically the same size and shape. 

 Owing to the fact that a large number of highly diversified forms were included in the 

 group of bacteria, considerable confusion existed before Koch devised his solid media 

 and his plate-pouring methods. The proof that each type of cell, such as the spherical 

 coccus or the elongated bacillus, came from a cell of the same type, a coccus or bacillus, 

 was of enormous benefit in straightening out the confusion and in eventually reconcil- 

 ing conflicting observations and opinions. While it was early recognized that the meth- 

 ods by which the bacterial cells are derived from the pre-existing cells might differ in 

 different species, two regular methods were definitely estabhshed: binary fission, 

 where one cell divides transversely into two new cells which eventually attain the size 

 and shape of the original; and spore formation, by which a single spore forms in a ba- 

 cillus, this spore subsequently giving origin to a vegetative rod like the original rod be- 

 fore sporulation begins. A more complicated cycle of development from conidia was 

 established for certain species which were differentiated from the simple bacteria ex- 

 hibiting transverse fission or spore formation as the "higher bacteria" and called 

 "streptothrix" or "actinomyces." 



Exceptions to these regular methods of reproduction of the bacterial cells were 

 frequently noted. With some species appearances were described which indicated 

 that new cells might rise from old cells by a kind of branching of the cytoplasm, this 

 phenomenon being described as "true branching" to distinguish it from the branching 

 seen in certain plants related to the bacteria, where the cells divide transversely and 

 eventually so crowd the sheath in which they are contained that this itself divides. 

 Knoblike protrusions from the bacterial cells were noted occasionally, and the sug- 

 gestion was made that these protrusions are in reality buds, capable of growth and de- 

 velopment into adult forms. Large, irregular, distorted elements were described in old 

 cultures, especially by Hueppe, who regarded them as true stages in the life-cycle of 

 the bacteria and named them "arthrospores." Occasionally more than one spore was 

 found in a single bacillus, and the idea naturally arose that spore formation may lead 

 to an actual increase in the numbers of the cells. Such double spore formation was ad- 

 mittedly very rare and generally doubted so that the thesis maintained by Kruse was 

 usually accepted, to the effect that spores represent resistant stages of bacteria like 

 the cysts of the protozoa which serve for the perpetuation of the species under adverse 

 conditions, but not for multiplication. Finally, with the flexible spiral organisms, the 

 spirochetes, differing from the ordinary bacteria in many of their characteristics, a pe- 



