HERBERT C. WARD 13 



Finally, Wolbach and Schlesinger' have brought to cultivation the micro-organ- 

 isms of Rocky Mountain spotted fever {Dermacentroxenus rickettsi) and typhus 

 {Rickettsia prowazeki) in tissue-plasma cultures. These authors have shown that the 

 parasite of Rocky Mountain fever shows a definite series of morphological changes 

 in ticks, from coccus to bacillary forms. Such observations suggest a somewhat more 

 complicated cycle of development than that accepted for the ordinary bacteria and 

 bring further evidence in favor of the view that binary fission and spore formation are 

 not the only methods by which the bacteria multiply. 



' Wolbach, S. B., and Schlesinger, M. J.: /. Med. Research, 44, 231. 1923-24. 



