230 THE PATHOGENIC FLAGELLATES 



exist in regard to this. Many are lymph or blood-dwelKng forms, 

 while some are neither parasitic nor commensal in their mode of life. 



Some forms may be both coelozoic and cytozoic. Tr. 'pallidum, for 

 example, is considered by some observers {e. g., Bandi and Simonella, 

 1905) to be a typical intracellular parasite, although usually found in 

 the lymph. Treponema gallinarum frequently leaves the blood serum 

 and penetrates the blood cells of chicks (Prowazek, Marchoux, and 

 Salimbeni). Sp. didtoni penetrates the egg of the tick Ornithodorus 

 mouhata and multiplies there (Koch, Carter), while Sp. microgyrata 

 var. Gaylordi is frequently found in the cancer cells of mice (Fig. 86, 

 p. 213). 



Closely connected with their habitat and mode of life in the host 

 is the possibility of transmission by insects, which, according to Liihe 

 ('06), are the definitive hosts of these forms. It is generally believed, 

 upon the basis of experiments made by Nuttall, that bedbugs convey 

 Sp. recurrentis from man to man, while Schaudinn found that the 

 organisms multiply within the body of this insect. Similarly, the 

 closely allied spirochete Sp. didtoni of tick fever was found by Dutton 

 and Todd ('07) to be conveyed by the bite of a tick Ornithodorus 

 moubata; they also showed that the larvae were capable of transmitting 

 the disease with the first feeding operation, while Koch ('05) described 

 spirochetes on the surfaces of ovaries and eggs of the insect and gave 

 strong evidence to indicate that they multiply there. This evidence 

 was fully confirmed by Carter ('07), who found the organism dividing 

 rapidly in the protoplasm and yolk of the egg (Fig. 91). Here, there- 

 fore, is a case of direct inheritance, in insects, of disease-causing organ- 

 isms. Treponema gallinarum and Sp. theileri are similarly trans- 

 mitted by ticks, the former by Argas miniatis, the latter by Rhipi- 

 cephalus decoloratus. Borrel and Marchoux, for the former, and 

 Theiler, for the latter, showed that multiplication likewise occurs here 

 in the bodies of the insects, and that the eggs may be infected and may 

 carry the organisms. 



Beyond simple division there seems to be no important life phase 

 in the bodies of insects; but this fact of multiplication is of consider- 

 able importance, as showing that the insect hosts are not merely 

 passive carriers, but are active agents in the transmission and distri- 

 bution of the parasites, and therefore are important agents in spread- 

 ing these spirochete diseases among vertebrates. Further research 

 will probably bring to light some conjugation process, but as yet nothing 

 of the kind is known. 



Schaudinn ('04), on the strength of his observations on the reduction 

 in size until almost invisible of Leukocytozoon ziemanni, after repeated 

 divisions, suggested that yellow fever might well be a disease due to 

 spirochetes. The now well-known agent of transmission, Stegomyia 

 fasciata, requires a period of twelve days before it is capable of giving 



