228 THE PATHOGENIC FLAGELLATES 



E. Form Changes and Life History,^ — Stability of form, due to 

 the firm body wall, is one of the characteristics of bacteria, while 

 polymorphism is equally distinctive of protozoa (p. 19). With the 

 spirochetes, some appear to be remarkably stable in form (e. g.,.Sp. 

 microgyrata, Sp. recurrentis, etc.), while others are highly variable 

 (e. g., Tr. pallidum). All seem to have a greater or less power of 

 agglomeration comparable with the agglutination of bacteria, and 

 indicating some physical change in the cell analogous, perhaps, with 

 the "miscible state" at certain periods of the life history of infusoria. 



Another matter of considerable importance in the structure of the 

 spirochetes is colony formation and the question as to the "unit" 

 individual. The number of nodes often varies within such wide limits 

 that the problem as to what constitutes a single spirochete cell has 

 a more than theoretical interest. Migula ('00) and Fischer ('03) 

 suggested that spirochetes may be composed of many units, a point of 

 view supported by the effect of abnormal conditions upon the spiro- 

 chete strings. Warming ('75) and Zopf ('82) described the fragmenta- 

 tion of the spirochete body after death in the cases of Sp. plicatilis and 

 Sp. gigantewn, while Laptschinsky ('80) claimed to have made out 

 such segmentation in the living cells of the former. These early obser- 

 vers may have been misled by the segmented appearance due to the 

 bands of chromatin in these forms. Similar observations, however, 

 have been made upon other forms, and under such different condi- 

 tions by competent observers that there is some justification for the 

 view that the "unit" consists of one node. Wechselmann and L5wen- 

 thal ('05) showed that long forms of Tr. pallidum, upon treatment 

 with mercury, break up into short forms with from one to four nodes. 

 Karlinsky ('90) found very short forms of Sp. recurrentis in the blood 

 of patients having previously had malaria, and these short forms, when 

 placed in normal blood, developed into normal spirals. In connection 

 with the same organism Afanassiew ('99) observed comma- and S-' 

 shaped forms in addition to the usual spirals, while Novy and Knapp 

 ('06) described the fragmentation of the long forms into such comma- 

 and S-shaped types under the action of phagocytes. Lowenthal ('05), 

 Krz3'sztalowicz and Siedlecki ('05), and others described minute types 

 of Tr. pallidum somewhat similar to those of the organism of relapsing 

 fever. 



In view of these facts, and in connection with the apparent disap- 

 pearance of spirochetes from the blood and organs of the body, the 

 possibility of the unit organism being much more minute than that 

 usually seen should not be overlooked. The actual life history, 

 furthermore, of no form has been satisfactorily worked out, and it is 

 quite within the bounds of probability that excessively minute stages 

 occur. Fertilization and tiie sexual phenomena, if they exist, are 

 unknown at the present time, and most of the attempts to formulate a 



