64 THE PERMANENT FORMS, OK SPORES. 



extremely susceptible to variations in the temperature and nutrient 

 medium. 



With these exceptions, only one spore is produced in the bac- 

 terial cell, in which event the spore formation doe's not result in 

 an increase in the number of the cells. It is scarcely necessary to 

 remark that it is not every cell that develops a spore, it being a 

 matter of frequent observation that individual cells in a bacterial 

 chain are sterile, leaving their neighbours on either hand to care 

 for the maintenance of the species. An attempt is made to re- 

 present this state of things in Fig. 19, which is a drawing of 

 Bacillus tumescens made from nature by A. KOCH (I.). 



51. Form and Size of the Spores. 



These characteristics vary of course in different species, the 

 spores of Bacillus subtilis, for example, being ellipsoidal and 

 measuring 1-2 //. in length by about 0.6 p, in breadth, whilst the 

 similarly shaped endospores of Clostridium butyricum are 2-2.5 \L 

 long and i.o /A broad. The general shape is oval, but there are 

 noteworthy exceptions to this rule. One of these is exhibited by 

 the Bacillus inflatus, which has already been frequently referred to. 

 As can be seen from Fig. 1 7, the spores of this microbe have the 

 form of an elongated cylinder, and are often curved in the shape of 

 a bean. With a breadth of about o. 7 p. the largest of them attain 

 a length of 3.8 /A, in which respect this species is as yet unrivalled. 

 We may here mention that in A. Koch's work, as also in Eisen- 

 berg's treatise, already alluded to, a number of spore measure- 

 ments are given. The duration of spore formation has been 

 determined by Prazmowski for Clostridium butyricum as 10 to 18 

 hours at 3o-35 C. 



52. The Conditions Influencing Spore Formation 



have been frequently investigated, but no generally satisfactory 

 elucidation has yet been obtained. H. BUCHNER (IT.), on the 

 basis of his studies, sought for the explanation in the exhaustion 

 of the supply of nutriment ; but this is contested by OSBORNE (I.). 

 TURRO (I.), on the other hand, sees the cause in the accumulation 

 of noxious transformation products, against which the vegetative 

 form seeks protection and the maintenance of the species by 

 developing the hardier reproductive spores. 



A. Koch established the fact that Bacillus inflatus in hanging- 

 drop cultures forms spores when a i to 2 per cent, solution of meat- 

 extract is employed as nutrient medium, but that they are not 

 formed if grape-sugar be added thereto. Clostridium butyricum 

 forms spores only in the absence of oxygen, whilst the morpho- 

 logically similar Cl. Polymyxa, on the other hand, produces them 

 only in presence of this gas. KOTLJAR (I.) found, in a microbe 



