630 APPLICATION OF METHODS OF BACTERIOLOGY 



organisms. It will suffice to say for our purposes that as 

 yet there is no agreement as to their exact status in the world 

 of living things. They appear to occupy a position some- 

 where between the bacteria on the one hand and the protozoa 

 on the other. 



A few of them are susceptible of cultivation under arti- 

 ficial conditions, and on these we possess at least the begin- 

 nings of an understanding, while for many others which 

 cannot be cultivated (or, at least, have not been) we know 

 little more than their gross morphological characteristics. 



A certain number of them are found in association with 

 particular diseases of man and of animals and are believed 

 to stand in causal relation to such conditions. 



Many more are found living free in nature and are 

 regarded as of no significance, insofar as disease production 

 is concerned. 



The definite causal relationship of a few of them to cer- 

 tain diseases is now generally accepted as proved. 



To the student of etiology three genera in particular of 

 the spirochaetacese are of special interest, notably: the spi- 

 ronema, the treponema and leptospira. 1 



Genus Spironema. To this genus belong all those species 

 or varieties that have been seen in the several manifesta- 

 tions of relapsing fever in man; such for instance as spi- 

 ronema carteri, spironema obermaieri, spironema novyi, 

 spironema duttoni; also those found in the so-called relaps- 

 ing fever of fowls, spironema gallinarum, spironema anserina; 

 also those found in the mouth, spironema buccalis, spironema 

 refringens, spironema vincenti and a number of others. 



They are seen as wavy, irregular threads with pointed 



1 See Noguchi, Jour. Exper. Med., 1918, vol. xxvii, p. 575. 



