No. 49SJ 



THE SPIROCHETES 



385 



and several minor or doubtful factors. The spirochetes 

 he believes to be distinct from trypanosomes in their less 

 highly specialized structure, which exhibits morphological 

 resemblance to bacteria. 



In the face of such conflicting testimony on these 

 morphological and physiological factors of primary im- 

 portance for the interpretation of the group, one is com- 

 pelled to seek collateral evidence to see if any can be 

 secured which is definite, even though not in itself deci- 

 sive. A few such indications are to be found among the 

 uncontroverted records of various investigators. It is 

 noteworthy that spirochetes resist culture in the media 

 which serve readily for bacteria in general, and herein 

 also resemble other protozoan saprozoites. 2 



Among indirect evidence one should note the work of 

 Marclioux. 3 It has been observed that spirochetes easily 

 lose their virulence. This author found that S. gal- 

 linarum, if passed through a series of birds, loses its 

 lethal power and infectivity. In nature, however, the 

 disease maintains its virulence, destroying entire broods 

 in countries where it is endemic. The persistent viru- 

 lence is thus seen to be related to the transmitting agent, 

 the tick Argas minialus. However, these ticks are in- 

 capable of increasing the virulence of a strain that has 

 become attenuated and merely maintain any strain at its 

 own level. These conditions do not resemble the action 

 of bacteria, but, on the other hand, do simulate the con- 

 duct of protozoa, which pass through part of the life cycle 

 in an intermediate host. 



Another indication of much importance was furnished 

 by Lingard in 1903 when he observed spirochetes in cattle 

 penetrating red blood cells. Prowazek describes and 

 figures in detail this occurrence in the fowl's blood where 

 the parasite, after entering the corpuscle assumes a coiled 

 or resting condition which he believes related in some 

 manner to the (supposed) developmental cycle in the 



