TEXT-BOOK OP BACTERIOLOGY. 193 



As already said, the spinosus does not possess any pathogenic 

 qualities. 



Spirilla. 



All the micro-organisms as yet treated of belong, morphologi- 

 cally, to the globe and rod bacteria, and we have not yet made the 

 acquaintance of a single screw-shaped bacillus. . This is not because 

 of their rare occurrence; on the contrary, they are very widely dif- 

 fused in nature. For instance, if we let the blood of oxen or sheep 

 stand for a considerable time, we will almost always find that in 

 the upper parts of it extremely long, briskly motile, strong, 

 well-formed spirilla are developed. Still oftener in the saliva of 

 the mouth, in intestinal contents, etc., one meets with short, simply 

 bent forms, which are commonly called vibriones, and which in 

 cover-glass preparations only appear as' bent bacilli. It is not till 

 they stretch themselves and begin to grow that one perceives how, 

 together with the bending, there is also a turning, a leaving of the 

 surface, and how the supposed rod in its development does not fol- 

 low its longitudinal axis alone (which would change it from the 

 semicircular to the complete circular form), but grows in a screw- 

 like or corkscrew- like fashion. 



An exact studj' of all these forms is attended with some diffi- 

 culties, inasmuch as the spirilla or vibriones almost without excep- 

 tion show very little inclination to develop on our artificial food 

 media, while,, as Weibel has found, highly-diluted food media are 

 much more to their taste than the concentrated ones which we or- 

 dinarily employ. 



"With these latter we have, nevertheless, succeeded in breeding 

 some members of the class of screw-shaped bacteria, and the in- 

 vestigator just mentioned has isolated quite a series of species 

 found in the mucus of the nose, the coating of the tongue, and par- 

 ticularly too in canal mud. 



Most of these appear only as short, bent rods or vibriones. 



The regular, or at least frequent, occurrence of long screws, on 

 the other hand, has hitherto been noted in only two micro-organisms 

 of this group, viz., in the Spirillum rubrum, discovered bj' E. von 

 Esmarch, and in the Spirillum concentricum, discovered by Kitasato. 



The former was accidentally found in the bacteriological exam- 

 ination of the putrid body of a mouse. Whether it has any direct 

 relation to the process of decomposition cannot as yet be stated 

 absolutely. 



These bacteria are tolerably thick, quite transparent, and pel- 

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