CHAPTER XXXIII 



THE SPIEOCHETE GROUP— THE GENERA TREPONEMA AND 

 LEPTOSPIRA, THE DISEASES SYPHILIS AND YELLOW 

 FEVER. 



The organisms which belong to this group are Yery 

 slender spiral forms, usually motile by means of sinuous 

 movements of the body. In many respects they closely 

 resemble the protozoa and it is a disputed point as to 

 whether they belong to this latter group or to the bacteria. 

 The group as a whole has not been studied until recent years 

 because of the difficulties in observation. It is only by 

 means of the dark field illuminator and by the use of 

 special stains that in the last two decades many of the 

 species belonging to the group have been recognized and 

 studied. 



Many diseases of man and animals are known to be 

 caused by organisms belonging to this group. Two will be 

 considered here. Syphilis caused by Treponema pallida 

 and yellow fever caused by Leptospira icteroides. In addi- 

 tion to the diseases just enumerated, there are the so-called 

 relapsing fevers and tick fevers of several types, caused by 

 organisms of this group in man. A similar disease in 

 chickens and geese is caused by a spirochete and is trans- 

 mitted from one bird into another by means of a fowl tick. 

 Similar tick-transmitted diseases have been described in 

 cattle, sheep and horses-. 



Treponema pallida 



Sjmonyms. — Spirochceta pallida, Spirillum pallidum. 

 This organism, the specific cause of the disease syphilis 

 in man, was first described by Schaudinn and Hoffman in 



397 



