TEXT-BOOK OF BACTEKIOLOGT. 1T9 



become well known to us through the investigations of Pasteur, 

 Fitz, van Tieghem, and particularly of Prazmowski. Although the 

 observations of these men were made at a time when the advan- 

 tages of a solid food medium were still unknown and when, conse- 

 quentlj-, some important means for testing and proving the results 

 elicited were wanting, yet we know sufficient about the micro- 

 organisms in question to be able to form a pretty comprehensive 

 idea of them. 



We know that they are large, broad rods with clearly-rounded 

 comers and often growing out into long chains. They have a lively 

 power of locomotion. They frequently proceed to sporulate, and 

 the spore-bearing cell always changes its previous form. It be- 

 comes inflated at the place where the spore forms, and the rods 

 thus swollen take a spindle-shaped appearance; they take the form 

 known as a Clostridium. AThen the spores begin to germinate,, the 

 membrane bursts at one end of the oblong spore, and the germ 

 becomes visible; the empty envelope of the young cell often remains 

 hanging for a considerable time. 



This Bacillus butyricus (also called Clostridium butyricum) be- 

 longs to the strictly anaerobic bacteria. It thrives only when com- 

 pletelj- cut off from oxj'gen and ceases to perform its functions the 

 moment air gains access to it. This is also the reason why the 

 attempts made to breed it artificiallj' have not yet led to satisfac- 

 torj' results. 



The Bac. butyricus has, under certain circumstances, the qual- 

 ity that parts of its cell-bodj" become of a deep indigo-blue or 

 blackish-violet color when they come in contact with an aqueous 

 solution of iodine. This is particularly noticeable when the bacilli 

 have grown on a medium rich in starch; young cells then become 

 fully blue, while older ones only change their color at certain of 

 their cross stripes. As this pecuUar reaction resembles that of 

 granulose, van Tieghem has taken occasion to describe the Bacillus 

 butyricus as Bacillus amylo-bacter. 



In solutions of starch, sugar, and lactic salts, Bac. butjTicus pro- 

 duces large quantities of butyric acid, developing at the same time 

 carbonic acid and hydrogen. It is the same in old milk, but the 

 sugar of mUk must have been previously fermented into lactic 

 acid, for the butyric-acid bacOli cannot bring about this last 

 change with their o^vn unassisted powers. They are, however, 

 able to slowly dissolve coagulated casein, and the importance of the 

 role which they are thereby called to perform in the organic world 

 seems to be even still more extensive. According to some observa- 

 tions, they are said to cause the putrid decomposition of vegetable 



