086 SUMMARY OF CURRENT RESEARCHES RELATING TO 



are stainable in a very short time. The staining is not diffuse but 

 delicate and differential, and shows that all bacteria in their early stages 

 are short uninuclear cells. The bacterial cell-membrane presents itself 

 under the Microscope as a thin smooth structureless sheath. In some 

 species there exists, immediately external to this, a mucous investment, 

 which is to be regarded not as part of the cell proper, but as an excre- 

 tion product therefrom. The chief part of the bacterial cell consists 

 of cytoplasm, differentiable into an outer deeply staining layer or 

 ectoplasm and a less or not stainable endoplasm. The nucleus forms 

 the centre of the cell, and, though usually round or oval, may be very 

 irregular in shape. In the spore-forming bacteria it is smaller and less 

 regular than in the non-sporing. 



Cell-division takes place just as in the cells of higher plants and 

 animals, and is preceded by nuclear fission, the constriction of the cyto- 

 plasm following immediately. In this way new members are developed, 

 and these become separated or may remain adherent. In the latter case 

 polynuclear rodlets or filaments arise. The isodiametric cells of a 

 bacterium which is to develop into a rodlet are easily distinguishable 

 from true spheroidal bacteria, by the delicate constitution of the invest- 

 ing membrane and the easy demonstrability of the nucleus. The wedge- 

 forms of the bacilli of the diphtheria group are mostly uninuclear cells, 

 the long rodlets and clubs being composite ones. When in a good con- 

 dition of nutrition the structural details of the vibrios of the cholera 

 group and also spirilla are complicated and indistinct, but in the atro- 

 phic condition they present a typical cell-structure and are uninuclear 

 cells. 



When spores develop in a bacterial cell, the cytoplasm in the 

 vicinity of an axially placed nucleus clears up and assumes an oval 

 shape. This spot increases in size, and assumes chromatophilous pro- 

 perties, and finally, by the formation of a membrane, becomes highly 

 refractive and difficult to stain. Spore-formation practically consists of 

 an intracellular incapsulation of the nucleus and of the thickened peri- 

 nuclear cytoplasm. The spore always possesses a centrally placed 

 nucleus, and in some bacteria the spore-membrane is clearly double. 

 The spore-plasma is homogeneous, but before germination becomes dif- 

 ferentiated into ecto- and endoplasm. In some bacteria the rupture of 

 the spore-membrane at germination is equatorial and in others polar. 



Albumen-forming Bacteria.* — Dr. Gerlach and Dr. Vogel obtained 

 seven species of albumen-forming bacteria from garden earth and stable 

 manure. The general characters of these bacteria are as follows. All 

 are short motile rodlets which stain with the usual anilin dyes. They 

 do not form spores. They grow on all the ordinary media ; they rapidly 

 liquefy gelatin, and do not form gas in the presence of grape-sugar or 

 nitrate. They thrive in liquid media which contain, besides the requisite 

 mineral substances, grape-sugar, glycerin, straw, lactic-acid-salts, &c, 

 as sources of carbon and saltpetre, ammonia-salts or urea as source of 

 nitrogen. When the nou -nitrogenous and the nitrogenous nutrient sub- 

 stances are absent, no noteworthy growth takes place. Hence the albu- 

 men-forming bacteria have not the capacity to utilise the carbonic acid 

 or the nitrogen of the air. On the other hand, they all have the power 



* Centralbl. Bakt., 2" Abt, vii. (1901) pp. 609-23. 



