150 INFECTION AND IMMUNITY 



the excreta. Even the spirillum itself is not easy to 

 see. A good microscope and a considerable degree 

 of skill in its use are required for the demonstration of 

 the slender spiral filaments in blood drawn from the 

 circulation of a relapsing-fever patient. Although 

 comparatively long and endowed with active move- 

 ments, they are only about one fifty-thousandth of an 

 inch in diameter. 



That the disease may be transmitted by direct con- 

 tagion, from individual to individual, has generally 

 been admitted by medical authorities. On the other 

 hand, the evidence on record shows that in well venti- 

 lated apartments and hospital wards the attendants 

 upon the sick and patients suffering from other dis- 

 eases are not very liable to contract the disease. 

 Where, however, the sick are massed together in in- 

 sufficiently ventilated hospitals, or when cases occur 

 in the overcrowded tenements of the poor, the trans- 

 mission of the disease to attendants and others ex- 

 posed to contagion is far more frequent. 



Up to the present time, attempts to reproduce the 

 spirillum of relapsing fever in a series of cultures 

 have not been successful. 



There is no evidence that climate or season has any 

 marked influence upon the prevalence of relapsing 

 fever ; the disease has prevailed in Siberia as well as 

 in India, and its preference for certain localities is 



