88 DISSOCIATIVE ASPECTS OF BACTERIAL BEHAVIOR 



THE CYTOLOGIC AL APPROACH 



The cytological approach to the problem of microbic dissociation has centered 

 mainly on the variable morphology of the bacterial cells and their nuclear appara- 

 tus. It has followed (especially in the morphological aspects) the lines laid down in 

 mycology at a much earlier date. Here the attempt has been made to discover, in the 

 peculiar bacterial elements often observed in cultures, the groundwork for an inter- 

 pretation of microbic heredity, involving modes of reproduction quite different from 

 simple fission. Most of the earlier studies dealt with the microscopical cell changes, 

 but without special reference to nuclear behavior. Later studies, and particularly 

 those of Almquist, Enderlein, and Mellon, have concerned themselves as well with 

 alterations in the nuclear apparatus. In view of the importance of the work dealing 

 with the nuclear changes, a few words must be said regarding later conceptions of th; 

 nuclear structure and the "chromatin" of the bacterial cell. The following represents 

 some of the essential features of Enderlein's' view which I believe we may accept as 

 reflecting the best knowledge now available regarding this important organelle. 



The nuclear unit (Mych) of the microbic cell possesses a spherical or oval form and, in 

 the coccus, often attaches itself to the inner wall of the cell, against which it may sometimes 

 be flattened. In cocci there is but one nuclear body while in all other forms of bacteria there 

 are two or more. The diameter varies between o.i and 0.25 /x. It contains no chromatin 

 and, with weak fuchsin, stains hardly any stronger than the cytoplasm of the cell. With 

 methylene blue it may remain practically unstained. 



The nuclear body is observable only when the cell containing it holds but little food sub- 

 stance in reserve. The latter commonly exists in the form of ultramicroscopic granules, the 

 trophoconia, and this substance represents the actual "chromatic" material of the cell. It 

 stains strongly because of its high content of nucleic acid and nucleo-proteins. The failure of 

 a cell to stain well with methylene blue is due to the absence of the food-reserve substance. 

 When the trophoconia bodies are abundant, their substance forms a dense aggregation about 

 the nuclear body, and the element so formed stains readily; this is the trophosome. If only a 

 light and thin layer of reserve substance clusters about the nucleus, this body becomes the 

 trophosomelle, which is smaller and more delicate. Neither of these bodies (trophosome or 

 trophosomelle) is the actual nucleus, however; they merely contain the nucleus as a central 

 granule. Some of the granular bodies earlier described for bacteria, such as the Much gran- 

 ules, the sporogenous granules of Ernst, and the metachromatic granules of Babes, are ac- 

 tually trophosomes or trophosomelles. Other granules appear to be c|uite different struc- 

 tures — sometimes the gonidia. They are all easily observable and often gram positive. If the 

 trophosome is situated at the end of a rod form, it is a "telotrophosome"; if at other points 

 in the cell, it is an "ascotrophosome." Moreover, to continue Enderlein's somewhat elabo- 

 rate but necessary terminology, if a cell is free from reserve substance (trophoconia), it is 

 an "atrophite." If it is merely poor in reserve substance, it is a "metatrophite"; if rich in 

 reserve, it is a "pliotrophite." 



When the reserve substance in a cell has been used up, as in bacteria that have been 

 starved (as in distilled water), the last remnant clings tenaciously about the nuclear body. 

 Large amounts of food-reserve substance, which may conceal not only the nucleus but also 

 the trophosomes, may be removed from the cell by alcohol. Under these conditions, when 

 properly stained, it is observed that, in coccus forms, only a single point takes the stain. In 

 rod forms, on the other hand, two or several such bodies take the stain. These are often at 



' Endcdein, G.: Bak'ericn-Cydogcnie. Bcriin, 1925. 



