26 



THE SMALLEST LIVING THINGS 



having whorls of greater amplitude though much fewer in num- 

 ber. Its chief characteristic is the presence of a relatively wide, 

 rigid ledge, known as the crista, which runs spirally about the 

 body from end to end and which is thought to correspond to the 

 columella characteristic of Spirochaeta. Like Saprospira it 

 reproduces by transverse division and by coccoid bodies. 



Cause Disease in Man and Beast 



The smallest examples of the spirochaetes — the Treponema 

 type — are frequently harmful parasites and are frequent causes 

 of disease in man and domesticated animals. Relapsing fevers, 

 tick fever, yellow fever, infectious jaundice, rat-bite fever, ve- 

 nereal diseases of man and other mammals, and blood diseases 

 of birds, are due to one or another form of Treponema. 



The species of this genus are all minute (from 2[x to 3(V) 

 and are so thin and delicate that, for the most part, they can be 

 seen only with difficulty (Fig. 14). This may be realized by 



Fig. 14— TREPONEMA 

 MTCROGYRATA 



A parasitic spivochaete which lives in 



diseased tissues of mice. The turns 



of the spirals are so close together 



that they can barely be recognized 



From a photomicrograph by the author 

 Magnification, 1000 



the fact that the minute organism, which is the cause of syphilis, 

 was not seen until 1905, in which year Fritz Schaudinn, a German 

 and one of the keenest observers among modern zoologists, dis- 

 covered it and named it Spirochaeta pallida, a name which he 

 later changed to Treponema pallidum (Fig. 15). Prior to this, 

 however, somewhat similar spirochaetes had been observed and 

 identified as Spirillum; one, named Treponema recurrentis, was 



