40 SPIROCHiETES 



the granule stage and may thus be transmitted in dust or on the 

 bodies of flies. Spirochceta bronchialis, causing a form of bron- 

 chitis, is probably transmitted in this way. 



There is a wonderful variation in the size and form of spi- 

 rochaetes and also in their mode of life. A few species are free- 

 living and of very large size, in fact almost visible to the naked 

 eye (i mm. in length), and there are many large species which 

 live as harmless commensals with various moUusks. The 

 disease-causing species (some examples of which are shown in 



iD 



Fig. 5. Types of parasitic spirochaetes. A, Sp. duUoni; B, Sp. novyi: C, Sp. 

 pallida; D, Sp. refringens; E, Sp. balanitidis; F, Sp. vincenti; G, Sp. icterohemor- 

 rhagim. X about 1500. (After various authors.) 



Fig. 5) are very much smaller, often being so delicate and slender 

 as to be hardly visible under the highest powers of the micro- 

 scope. Not all the small spirocheetes of vertebrates are patho- 

 genic however; two species occur almost invariably in the 

 human mouth, living on the tartar of the teeth and about the 

 roots of the teeth, and yet, normally at least, cause no ill effects. 

 One of these inhabitants of our mouths, Sp. buccalis, is a relatively 

 short blunt species, but the other, Sp. dentium, is excessively 

 slender, and practically indistinguishable when living from the 

 spirochete of syphilis. Other harmless spirochsetes occur in 

 various stagnating secretions or excretions of the body, about the 

 tonsils, and in the intestinal mucus. 



Spirochaetes and Disease. — There is some question about 

 how many distinct human diseases are caused by spirochaetes. 

 The mere presence of spirochaetes in sores or diseased tissue is 

 not sufficient reason for believing'that they are the direct cause 

 of the diseased condition, for, like many bacteria, they are often 

 found in exposed sores which are known to .be due to other 

 causes. Spirochaetes are often found associated in sores or ulcers 

 with certain kinds of bacteria, and both bacteria and spirochaetes 



