2G6 THE PATHOGENIC FLAGELLATES 



disappear from the digestive tract of the fly within three or four days 

 after feeding. Others, on the other hand, notably Gray, Mipchin, 

 Tulloch, have found abundant multiplicative forms in the anterior 

 part of the digestive tract, and encysted forms in the posterior part 

 (proctodeum). These observers hold, and many others on a priori 

 grounds alone support them, that important developmental stages of 

 Trijp. gamhiense will yet be found outside of the human body. That 

 such an external life is obligatory for trypanosomes in general is 

 disproved by the fact of direct transmission in the case of Tryp. 

 cquiperdum, where all of the developmental phases must take place 

 in the mammal. 



A very strong argument in favor of the advocates of an external 

 cycle are the observations, by different investigators, of the life history 

 of trypanosomes infecting other than mammalian hosts. Keysselitz 

 ('06), for example, found both multiplicative and propagative (terms 

 used in Doflein's sense) development of Trypcmoiplasma borreli in the 

 digestive tract of the leech Piscicola geometra; Prowazek ('05) found 

 similar phases of Tryp. lewisi in the gut of the louse Hematopiims 

 spinulosus; but these, and all of the subsequent observers, go back to 

 the classical work of Schaudinn ('04) upon Tryp. noctuw of the owl 

 for their models, a work fully confirmed by the brothers, Et. and Ed. 

 Sergent ('05). 



The mosquitoes used by Schaudinn and by the Sergents were raised 

 from eggs and larv£e, so that previous infection was thereby excluded, 

 the chances of their being infected by inheritance, which Novy, Mac- 

 Neal, and Torrey ('07) claim in criticism, being so remote that the 

 results are by no means vitiated by this possibility.' 



Mosquitoes which are allowed to feed upon owls (Glaucidium 

 noctiice) infected with Tryp. noctuw take male and female trj'pano- 

 somes into the gut with the blood. Here fertilization takes place in the 

 manner described by MacCallum ('99), in connection with the para- 

 site Hemoproteus (Halteridium) of the American crow. The so-called 

 halteridium, therefore, of the owl is only a stage in the life history of a 

 trypanosome, the microgametes being formed in response, apparently, 

 to the changed conditions of temperature and chemical composition 

 in the new environment. The fertilized gamete, called ookinete, or 

 copula, by Schaudinn, develops into a trypanosome which may be 

 male, female, or indifferent, according to the changes undergone by 



1 Schaudinn (loc. cit., p. 390) states: Die Zucht der Miicken, die Art der Infection, die 

 Blutuntersuchungen usw. erfolgte in derselben Weise wie bei meinen Malariastudien. For tlie 

 latter work he made use of carefully watched mosquitoes bred from the egg. Knowing from 

 personal experience Schaudinn's keen zoological sense, quickness of vision, and remarkable 

 talent in handling protozoa of various kinds, I personally do not share in the skepticism 

 which has grown up in regard to his observations, and, although not always agreeing with 

 his interpretations, I find much more reason for accepting his conclusions than those of his 

 many critics which are based mainly on a priori arguments or upon negative results with 

 artificial culture methods, which, at best, are unnatural media for protozoa. 



