I SPIROCHAETES 77 



There does not appear to be any concentration of the particles of 

 nuclear material, which are scattered throughout the body, to form a 

 definite nucleus. Reproduction takes place so far as is known simply 

 by transverse fission. 



The first Spirochaetes to be discovered and described — so far back 

 as 1833 (Ehrenberg) — were free living creatures but the species of greatest 

 practical interest have taken on a parasitic mode of life. One group of 

 these (Cristispira) are found in the alimentary canal of Oysters and 

 other Pelecypoda (p. 267) and being of relatively large size and easily 

 obtainable are especially convenient for laboratory study. They may 

 be nearly always found in the " crystalline style " of freshly collected 

 specimens of the common fresh-water mussel (Anodonta). 



Of special human interest are the spirochaetes — of very minute size 

 — which live as parasites in the body of man and other vertebrates. 

 Certain of these {Spiroschandtnnia) inhabit the blood and cause fever, 

 e.g. in fowls and geese or in man. In man the disease produced is the 

 well-known Relapsing or Intermittent Fever which occurs in various 

 parts of the world. 



The common relapsing fever of tropical Africa is associated with 

 the presence, in the blood, of S. duttoni — a spirochaete measuring 

 about 14 /x in length. Infection is carried by a species of Tick — 

 Ornithodorus moubata — common in huts and camping grounds. When 

 infected blood is swallowed by this animal the spirochaetes instead of 

 being digested multiply rapidly and spread throughout its body. The 

 infected tick apparently does not inoculate the spirochaetes into a new 

 individual directly by its bite as one might expect. What happens is 

 that excretory material containing spirochaetes exudes from its anal 

 opening and, spreading over the surface of the skin, gets into the 

 wound. 



Amongst other tissues the eggs of the tick are penetrated by spiro- 

 chaetes, with the result that the young ticks of the next generation are 

 infected and are capable both of causing infection themselves and of 

 passing on the infectivity to their progeny. 



The type of Relapsing Fever once common in Western and still 

 occurring in Eastern Europe is brought about by the presence of a different 

 species of spirochaete {S. recurrentis or obermeiert) which may be dis- 

 tinguished from S. duttoni by its smaller size (7-10 yu). Observations 

 carried out in Northern Africa on what appears to be the European type 

 of Relapsing Fever have shown that the infective agents here are not 

 Ticks but Lice. When the louse has ingested infected blood the spiro- 

 chaetes gradually disappear from its alimentary canal and at the end 



