834 



THE AMERICAN NATURALIST |3 ol. XL 



disease rapidly over a wide area of country. The larva creeps 

 on an infected animal, sucks some of its blood, drops off, lies among 

 the roots of the grass, and passes its first moult becoming a nympha, 

 then an imago, in either of which latter stages it may infect a 

 healthy animal by creeping from the grass. 'J'he tick is very 

 hardy and may survive with its infection for a year, but after a 

 year or fifteen months the infected ticks are all dead and healthy 

 cattle may enter the field without risk. 



Wide Geographical Disirihution. — Piropla.^ina hif/cmininn simi- 

 larly causes the 'Texas' or 'red-water fever' of our Southern 

 States; it is conveyed by a tick. The germs are latent and the 

 blood of an animal which has recovered from Texas fever remains 

 infective; thus apparently healthy cattle may infect imported 

 susceptible cattle. SiK'h latency has an important bearing upon 

 the theory of natural extinction as caused by similar germs. The 

 geographical distribution of this species of Piroplasma is very 

 wide; first discovered in North America, it is now epidemic through- 

 out most of South Africa. Although accjuiring immunity, it is the 

 domesticated native Bovidie which act as reservoirs of the disease 

 in contrast to the tse-tse fly disease in which the wild Hoviche act 



in ihr a;liili ^ta-c. A> in rlic case ,»f 'lV.\a> fever in (•attle, SO the 



infection ihronu'liont their hve>. The .;,ine is true anioiiu- the 

 ( arnivora of the l'n-n,>/asn>a , n>u.. .pread l>^ the .lo^^ tiek , //,r„.n- 

 pln/salis Irarhii). The blood <.f r.-eovere/l aniniah remains in- 

 fectivt>. 



E.rternnna(ion of Wild Uumimwh. The rin.K-rpeM or cattle 

 disease has been the greatest destroyer of the wild African quad- 



