30 OUTLINES OF BACTEEIOLOGY 



small blunt points (Fig. 4=7 b). With regard to the size of these 

 structures the following figures given by Gottheil for the spores of the 

 soil-bacteria examined by him, will serve for this purpose : 



LENGTH. 



Bac. ruminatus, 1 -5-1 -7 ft. 



,, tumescens, - 2-5-3*0 /x. 



graveolens, - - 1 -9-2*5 /x. 



,, petasites, 1 -7-2-2 fi. 



Ellenbachensis, 1 -7-2-2 //. 



mycoides, 1*4-2 *2//. 



subtilis, - 1-7-1 -9 fi. 



pumilis, - 0-94-1 -52 /z. 



,, carotarum, 1 -31-2-2 //. 



fusiformis, diameter, 1-3-1 -8 /*. 



The spores of Sarcina ureae measure 1-1 J/A in diameter. 

 Contents of the Endospore and Conditions of Spore-formation. The 

 smallness of the spore and its thick, almost impenetrable outer mem- 

 brane, make it impossible to investigate the contents very closely, 

 but we are sure that the spore, like all similar structures, will contain 

 dense protoplasm, and enough food material to give it a start in 

 germination ; for, given the necessary moisture and temperature, spores 

 will germinate on a barren medium, e.g. a jelly made of gelatine and 

 water only. A large number of bacteria never, so far as we know, 

 form endospores, but it is doubtful whether they are never 

 under any circumstances able to form them. Many investigations 

 have been conducted with the aim of ascertaining the conditions 

 which influence spore-formation. In the case of Bac. inflatus it has 

 been found that a 1*2 per cent, solution of meat extract in the nutrient 

 medium has a favourable influence, whereas grape sugar has quite 

 the opposite effect. Another and anaerobic species (Clostridium 

 butyricum) forms endospores only when growing in an atmosphere 

 devoid of oxygen, while, on the contrary, Bac. anthracis, Bac. subtilis 

 and several others form these spores only if oxygen is present. The 

 author has found that a very slight percentage of acid influences 

 unfavourably the formation of spores in the case of Sarcina ureae. No 

 one has yet, despite many attempts, been able to cause a species to 

 form spores, if the species does not normally do so, though on the 

 other hand it is not difficult to prevent spore-formation in a species 

 which normally forms spores. 



Most sporogenous species, growing on solid nutrient media, com- 

 mence to form spores on the second day after inoculation, though in 



