WHAT ARE BACTERIA ? 37 



These so-called arthrospores of the cholera bacillus do 

 not, however, give the ordinary reactions of spores, nor 

 are they any more resistant to the action of heat and 

 germicidal agents than the vegetative forms themselves : 

 they must therefore still be looked upon as pseudo-spores. 

 True spores, then, appear to be special protoplasmic cells, 

 which are first developed in the mother cells and are then 

 surrounded by a very thin, but hard and dense membrane. 

 It is this dense covering that protects the delicate proto- 

 plasm within, against the action of the numerous destructive 

 influences to which the spore is exposed. 



If this structure be borne in mind, it becomes evident that 

 dry heat must necessarily be less efficacious than moist, in 

 determining the destruction of the spore. Dry heat causes no 

 swelling of the protoplasm within, whilst moist heat causing 

 swelling brings about rupture of the softened membrane by 

 pressure from within, and the unprotected protoplasm, exposed 

 under most unfavourable conditions, is at once rendered inert. 

 It appears probable that this process of expansion from 

 within also comes into play whenever spores are placed 

 in conditions favourable to their development, i.e., when 

 they are placed in a warm medium in which are present both 

 nutriment and moisture. 



The first change then noticed is that the clear, strongly 

 refractile protoplasm becomes cloudy or granular, the dark 

 outline is not quite so prominent and the clear boundary 

 line or limiting membrane appears to swell somewhat, 

 and the spores gradually assume the form of an ordinary 

 vegetative cell. In some cases, however, as soon as the 

 spore begins to swell, the delicate outer sheath may be seen 

 to split either longitudinally as in the Bacillus amylobacter, 

 or across the middle as in Bacillus subtilis. In either case 

 there is a swelling of the softened gelatinous layer which 

 causes the removal of the firm membrane. This thin, firm, 

 delicate membrane may come away in the form of two 

 separate cups, or there may be simply a transverse slit 

 through which the germinating spore escapes. Having 

 once made its way from the membrane, vegetative division 

 at once sets in, the segmentation always taking place at 



with the fluid almost to boiling point for ten or fifteen minutes. The 

 after procedure is as above. The spores most difficult to stain are those 

 of the bacilli of tuberculosis, and of typhoid fever. 



