16 BACTERIAL INVASION 



in man, and in fowls, and Rocky Mountain spotted fever 

 in man, all of which are carried by similar organisms, and 

 species of Argas and Ornithodoros. 



It is evident, then, that these arthropod-borne diseases 

 are coming more and more into prominence, especially in 

 connection with tropical diseases, and Manson goes so far 

 as to say that in parasite-ridden Africa bacterial disease 

 is a comparatively negligible quantity. Again it has been 

 pointed out that in the United States alone the annual 

 loss to cattle breeders through these tick diseases is already 

 known to amount to more than eight million pounds sterling. 

 Other blood-inhabiting parasites, such as spirochaetes and 

 organisms of the piroplasmal form, are all carried by these 

 arthropod hosts. The spirochaetes found in rats, fowls, 

 geese, cattle, sheep, horse, the bat, and man, appear to be 

 transmitted in this way, as do also the piroplasmata associ- 

 ated with Redwater fever in cattle and sheep, Texas fever 

 in cattle, Heart water fever, malignant jaundice in the dog, 

 biliary fever in horses, mules, and donkeys. Monkeys are 

 also affected by piroplasmosis, transmitted apparently by 

 similar carriers. It is evident, then, that a careful study 

 of the life-history, not only of the parasites themselves, but 

 of the arthropod carriers of these organisms, will, in the 

 near future, add considerably to our stock of knowledge 

 of the diseases both of animals and man. No account of 

 this aspect of disease in animals and man would be com- 

 plete which did not include some notice, however short, 

 of the parasitic amoebae. At one time it was supposed that 

 these amoeboid organisms were of little importance, cer- 

 tainly from the pathogenic point of view. It is now being 

 realised, however, that these simple amoeboid parasites 

 have a much wider distribution and a much more important 

 role in the production of disease in man and animals than 

 was at one time supposed. These amoebae, first brought 

 into prominence in connection with dysentery, appear to 

 multiply not only by fission, but also by a process of internal 

 division corresponding closely with spore-formation. Under 

 certain conditions, they assume what Geddes calls the rest- 

 ing or cystic stage. Walker (Jour. Med. Res., Boston, 

 vol. xvii., 1907-8, p. 379) describes no fewer than eleven 



