TIIK CONDITIONS INFU'KNCINC; SI'OIIK FORMATION 49 



and water of the Bay of Naples. Tlio. spirilla, as Mriiui \i SI:R (\.) has shown, 

 are extremely susceptible to variations in the temperature and nutrient medium. 



With these exceptions, only one spore is produced in the bacterial cell, in 

 which event the spore formation does 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 represent this state of 

 things in Fig. 19, which is a drawing ot 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 /z in length by about 

 0.6 IJL in breadth, whilst the similarly shaped endospores of Clostridium butyricum 

 are 2-2.5 V- l n g an( ^ 1>o P Droaa ". 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. 17, 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 0.7 /* the 

 largest of them attain a length of 3.8 /z, in which respect this species is as yet 

 unrivalled. We may here mention that in A. Koch's work, as also in Eisenberg's 

 treatise, already alluded to, a number of spore measurements are given. The 

 duration of spore formation has been determined by Prazmowski for Clostridium 

 butyricum as 10 to 18 hours at 3o-35 0. 



52. The Conditions Influencing- Spore Formation 



have been frequently investigated, but no generally satisfactory elucidation has 

 yet been obtained. H. BUCHNER (II.), 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 

 morphologically similar CL Polymyxa, on the other hand, produces them only in 

 presence of this gas. KOTLJAR (I.) found, in a microbe named Bacillus pseud- 

 anthracis, that spore formation was influenced favourably by violet light but 

 unfavourably by red light. 



Past experience has shown that the formation of endogenous spores is 

 confined to the rod-shaped species (bacilli). This observation has been utilised 

 in the classification of bacteria, as will be seen in 69. The reports to the 

 contrary found in the literature of the subject lack the force of proof, since they 

 ignore the fact that the sporous nature of the growths seen to originate in the 

 cocci has been demonstrated by germination tests. 



53. Resisting- Power of the Endospores. 



The forms in question are endowed with the character of reproductive cells, 

 since they are able to withstand those adverse conditions which would inevitably 



