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THE AMERICAN NATURALIST [Vol. XLII 



fered as additional proof of the bacterial nature of the 

 form with which they experimented, and finally they 

 record, the absence of a tendency to form layers around 

 each air bubble, which is a very characteristic reaction 

 for trypanosomes. Novy and Knapp conclude thus : 



"The several tacts which have heen brought out under the preceding 

 headings point clearly to the non protozoal nature of S. ohermeini. 

 We must conclude, therefore, that the 8. obermeieri belongs to the 

 bacteria and more especially to the Spirillacea?. As pointed out, the 

 same conclusion has been reached by Borrel as regards ijaUinarum 



and S. gallinarum. The facts brought out in this study point so con- 

 clusively to the bacterial nature of the organism's that there can be 

 little or no doubt of the correctness of the conclusion arrived at. 

 With the recognition of this proof it follows that insect transmission 

 is no longer a criterion of the nature of an organism." 



Radical as is this critique of the animal theory of 

 spirochete relationship, it has not been accepted as deci- 

 ding the question, and has only provoked further discus- 

 sion of the problem. Referring first to the question of 

 insect transmission, it may be said that Koch has shown 

 that the spirochetes multiply in the eggs of ticks and 

 Carter that they undergo there changes as yet unex- 

 plained which may substantiate the claim of another 

 cycle. Several investigators have found that in experi- 

 mental animals they pass through the placenta from the 

 maternal circulation to the fetal, although they undergo 

 no changes consequent to this transfer. These observa- 

 tions do not accord with known facts concerning other 

 bacteria. 



Almost at the same time there was published an ex- 

 ceedingly careful investigation into the structure and de- 

 velopment of the fowl spirochetes by Prowazek, with an 

 appendix on a species from -Anodon by Keysselitz, in 

 which both authors come to conclusions diametrically op- 



