24 



THE SMALLEST LIVING THINGS 



longing to different genera, under the names of Spirochaeta, 

 Saprospira, Cristispira, and Treponema, the last of which is suf- 

 ficiently diverse to have been split into a number of sub-genera 

 by different observers. 

 The first two of these 

 genera are not para- 

 sitic, but may be found Fig. n— spirochaeta plicatilis 



in Stagnating fresh and An inhabitant of poluted water. Only part of a specimen 



salt waters. They have 

 no particular impor- 

 tance to man, but prob- 

 ably play some part in causing decay of dead animal and plant 

 matter. 



is shown in this drawing made by the author 



From a photomicrograph by Marguerite Zuelzer 

 Magnification, 1500 



Types and Species 



Spirochaeta plicatilis is not uncommon and gives the impres- 

 sion of an actively undulating microscopic snake (Fig. 11). It 

 is distinguished by the possession of an axial bar, called a 

 columella, which runs from one end to the other, and around this 



Fig. 12— SAPROSPIRA 



A harmless non-parasitic spirochaete 

 from stagnant water. The granules 

 down the body are like bacteria 

 spores, but are called "coccoid" 

 bodies 



From a photomicrograph by the author 

 Magnification, 800 



bar the protoplasmic body coils like a spiral staircase about its 

 newel post. It shows very few other structures, and no nuclear 

 differentiation' or specializations can be distinguished in it beyond 

 the presence of very fine granules, known as chromatoid granules, 



