698 



SCIENCE 



[N. S. Vol. XXV. No. 644 



the basis of a few individual cells. For 

 example, Woodcock in his review of the 

 hffimoflagellates enumerates no less than 

 forty-eight species of Trypanosoma and 

 adds two additional ones as questionable. 

 I do not wish to be too severe, but I imagine 

 it would be nearer the truth had the ac- 

 count been of two species and forty-eight 

 questionable ones. In this group species 

 are based for the most part on unmeasur- 

 able differences in structure; often indeed 

 no such differences even can be made out — 

 but species are defined on strictly physio- 

 logical characters, such as life in different 

 hosts, inability to live on certain culture 

 media, different reactions towards immune 

 sera, etc., none of which are sufficiently 

 characteristic of species, although they may 

 well indicate specific differences. 



In very few cases has the life history of 

 the trypanosome been made out, but the 

 work of Sehaudinn, Keysselitz and Prow- 

 azek indicates that we have to do with 

 digenetic forms, while Novy's conclusions 

 are the reverse. It seems to me that the 

 culture method can not be relied on abso- 

 lutely in the testing of protozoan species; 

 to cultivate parasitic protozoa on media 

 is to cultivate them in one phase only of 

 their life history, and since the most im- 

 portant phases have never been seen in the 

 cultivated forms it is probable that the 

 period of youth of the individuals is the 

 best for cultivation. Inability to live in 

 the same mediimi is no test of a good spe- 

 cies. There are many species of protozoa 

 which live both in salt and in fresh water; 

 either if transferred suddenly to the other 

 medium would die, but either could be 

 gradually trained to live in the other me- 

 dium. So it is, as I believe, with Trypan- 

 osoma, and the multiplication of species 

 here is, to my mind, only evidence of our 

 ignorance of their life history. 



What is true of Trypanosoma is even 



more evident in the case of Spirockoeta. 

 Here, every month or so, some student of 

 the group describes a new species of Spiro- 

 chcBta before we have found out even 

 whether the genus to which it is ascribed 

 belongs to the Schizomycetes or to the Mas- 

 tigophora. Again the variations in struc- 

 ture of the various spirochagtes are so great 

 that if they were all true we should have 

 to make new generic names to hold them. 

 8. ohermeieri, for example, has the chro- 

 matoid granules of a bacillus, it reproduces 

 by transverse division, and is, in its mor- 

 phological characters much more like the 

 spirilla type than like the flagellate forms. 

 8. plicatUis, on the other hand, has longi- 

 tudinal division, a periplast membrane and 

 nucleus similar to that of the male trypano- 

 some, according to Prowazek. 8. pallida, 

 finally, has flagella, and reproduces by 

 longitudinal division according to Sehau- 

 dinn, and has a single nucleus according 

 to Sehaudinn, Herzheimer, Krzyztalowicz, 

 Siedlecki and Forrest, and trypanosome 

 phases according to Siedlecki. 



Out of this heterogeneous collection it 

 would seem to me that 8. ohermeieri might 

 well be a spirillum while the rest that I 

 have mentioned may be Spirochceta. What- 

 ever they are, it is quite evident that we 

 are here in territory which lies between the 

 two divisions of schizomycetes and mastigo- 

 phora and to tell whether a given Spiro- 

 chceta is a plant or an animal is only an 

 academic matter after all. What we really 

 want to know is the life history of the indi- 

 vidual and the form changes through which 

 it passes. When these are ascertained the 

 genera, families, orders and classes, or 

 kingdoms, will take care of themselves. 



The Morphological Diagnosis of Pathogenic 



Protozoa: James Ewing. 



A review of protozoan morphology shows 

 that all these organisms at some stages of 

 development assume very characteristic 



