CHAPTER IV 



THE SPIROCH^TES : BORDER-LINE ORGANISMS 

 BETWEEN PLANTS AND ANIMALS 



AMONG some of the most interesting lowly 

 organisms are the spirochaetes, which, like 

 some flagellates, either live freely in water, or inhabit 

 the digestive tract of many animals, or are found in 

 their blood. When they adopt the parasitic habit 

 in the blood, they can become deadly to man and 

 other vertebrates. The spirochaetes have already been 

 noted (Chapter I., p. 10) as presenting a good example 

 of gradual adaptation to parasitism, and now more 

 may be added as to their build, life-history, and 

 importance. 



The spirochaetes are a group of organisms with a 

 history. Lying as they do on the border line between 

 animals and plants, they have been the centre around 

 which much controversy has raged. It will be the 

 endeavour of the present writers (who have worked 

 personally on many members of the group) to give 

 an account of these organisms that shall be as 

 non-controversial as possible, and which will consist 

 of facts and not the speculations so fashionable 

 nowadays. 



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