34 THE BACTERIAL CELT, 



we are indebted to SCHEWIAKOFF (I.), according to whom each of these small 

 enclosures contained in the honeycomb cells possesses a thin skin, the presence 

 of which can be convincingly demonstrated by pressing the preparation under 

 a cover-glass, whereupon the skin bursts, without, however, its contents being 

 dispersed. The latter can therefore only be of a solid and not of a fluid nature. 

 The chemical nature of the skin is unknown ; it does not give the cellulose 

 reaction. So far as the composition of the granular contents is concerned, the 

 named investigator has identified therein by micro-chemical means potas- 

 sium, calcium, and oxalic acid, in addition to the indeterminate organic matter. 

 In their behaviour, more closely investigated by WAHRLICII (I.), towards 

 colouring and solvent reagents, these enclosures in the central body of the 

 bacterium resemble those granular constituents of the cell nucleus of higher 

 plants known as chromatin granules, on account of their high power of absorbing 

 colouring matters. On the other hand, the reticular mass of the central body 

 resembles in point of structure and micro-chemical reaction the lignin of the 

 nuclear framework of the cells of higher plants. 



These observations led BtiTSCHLi (II.) to the opinion that the central body of 

 bacteria should be regarded as the (comparatively large) nucleus thereof whilst, 

 on the other hand, the above-named parietal layer corresponded to the cytoplasm 

 of the cells of higher plants a conception which has not withstood the test of 

 criticism. 



The structure of the parietal layer has not yet been determined with 

 certainty. Sundry observations, however, indicate that it exhibits a radial 

 honeycomb appearance. It is in this layer that the colouring matter of the 

 chromogenic bacteria is lodged, whereas the granules of sulphur in the sulphur 

 bacteria are located in the central body. The individual species of the genus 

 Granulobacter established by Beyerinck to which belong the instigators of the 

 butyric acid and butyl alcohol, &c., fermentations under certain conditions of 

 culture store up in their interior copious supplies of granulose, owing to which 

 circumstance they are stained a deep blue by iodine. It should be mentioned 

 that \V. MIGULA (I.) could not detect any honeycomb structure of the cell plasma 

 during his researches into the structure of the Bacillus oxalaticus, discovered by 

 Zopf. 



It may perhaps be useful, though not exactly necessary, to remind the reader 

 of the well-known botanical fact that the living plasma strives to prevent the 

 access of colouring matters. In this connection, also, the behaviour of the various 

 kinds of fission fungi differs. Some of them exhibit merely a slight resistance, 

 and absorb colouring matter without their vitality being impaired, as Birch - 

 Hirschfeld established with respect to phloxine red in the case of the typhus 

 bacillus. In the majority of instances, however, this resistance is so great that 

 the cells must be killed before they can be stained. On this account most of the 



-.inir solutions employed for bacteriological purposes contain additions (e.g. 



alcohol) destructive to the vitality of the cell, which being accomplished, the 



plasma readily absorbs the colouring matter. According to the researches of 



I )i:i:YKrss (I.), it is not the true albuminoid matter, but the nuclein (also a 



ituent of plasma) which fixes the colour. 



Thanks to the care bestowed on the subject by medical bacteriologists specially 

 iiit'-iv>trd therein, the art of staining bacteria has reached a high degree of 

 perfection during the last few decades. Exhaustive directions thereon are to 

 I"- found in Ih iprata ( 1.) handbook and EISEXBERQ'S (1.) treatise, and BKKMIKI.M 

 (I.) lias issued a very cheap book highly useful for laboratory work. In 

 Physiology the examination of the bacteria being usually performed 

 on the living. un>1 lined organism-, the aid of st linini: is seldom required; the 

 principal occasions being when so-called cover-glass preparations have to be kept 



