CHAPTER IV 

 SPIROCH-ffilTES 



General Account. — On the vague unsettled borderline be- 

 tween Bacteria and Protozoa there is a group of organisms which 

 are waging a frightful war against human life and health. These 

 organisms, commonly known as spirochaetes, when first discovered 

 were supposed to be of bacterial nature. Later, for many ap- 

 parently valid reasons, they were thought to belong to the Pro- 

 tozoa, but one by one these reasons for looking on them as animals 

 rather than bacteria are falling away and many biologists at the 

 present time relegate them to their old place among the Bacteria. 

 They still serve as a bone of contention, however, between bac- 

 teriologists and protozoologists, and at present we can only look 

 upon them as occupying an intermediate position between the 

 Bacteria on one hand and the Protozoa on the other. 



Like Bacteria the spirochaetes lack any distinct nucleus; their 

 multiplication is commonly by transverse division, although the 

 more typically protozoan longitudinal division has also been 

 claimed for them by some investigators; and no unquestionable 

 conjugation or other sexual process has been observed. Like 

 Protozoa, on the other hand, some of the spirochaetes have a 

 membrane, the " crista," which reminds one somewhat of the 

 undulating membranes of trypanosomes; they react to certain 

 stains and chemicals in a protozoan manner; and they multiply 

 in a specific intermediate host which serves as a means of trans- 

 mission to a new host. Until recently it was believed that some 

 spirochaetes passed through a distinct phase of development in 

 such intermediate hosts as ticks or bedbugs, but some doubt has 

 been cast on this, and it is now the commonly accepted belief 

 that the organisms live and multiply in the body of a tick or 

 insect just as bacteria do in artificial cultures, without going 

 through any phase of their life history which does not at least 

 occasionally occur in the vertebrate host. 



Spirochaetes are excessively slender threadlike animals, spirally 



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