THE PATHOGENIC TRYPANOSOMES 549 



tract of the mosquito arranged in rosettes, with sometimes the anterior 

 ends, sometimes the posterior ends, directed towards the centre of the 

 rosette. The next stage of development takes place when the parasites 

 by the mosquito's bite reach the blood of the vertebrate host, and it is 

 in connection with this stage that Schaudinn's observations are very 

 far-reaching. The indifferent forms by this time, by repeated longi- 

 tudinal division, have become small. In the owl they attach them- 

 selves to red blood corpuscles, which they penetrate, and, assuming a 

 halteridium form, grow in size for twenty-four hours ; they then leave 

 the cells, elongate, again assume the flagellate form, move freely in the 

 blood till the next night, when they again enter fresh cells. This cycle 

 is repeated for six nigiits, the organism gaining in size with each sojourn 

 in a corpuscle. When the full size is thus attained, repeated longi- 

 tudinal division occurs, and when the smallest forms are again reached 

 the intra- cellular/ cycle recommences. The largest female forms prob- 

 ably cannot pass through the mosquito's proboscis, but when small 

 forms reach the owl they enter the red corpuscles. They assimilate 

 food material, and appear not to migrate so frequently as the indifferent 

 forms. They lose their capacity of assuming the free trypanosoma 

 form, and ultimately their capacity of migration, so that they are 

 found lying surrounded by the remains of the last cell they entered. 

 The male forms when they reach the blood of the host rapidly die, and 

 the microgarnetocytes are always recruited from the indifferent forms, 

 or from parthenogenesis of the female forms. 



It may be said that according to Schaudinn the trypanosomes gain 

 access' to the tissues of the mosquito by perforating the intestinal wall, 

 and, passing through the body till they reach the wall of the pharynx, 

 they burst through this, and are in a position to be ejected when next 

 the insect bites. 



Such are the views put forward by this observer on the cycle 

 of life-history of the Tr. noctuse. It will be recognised that 

 the essential point is the occurrence, both in the vertebrate and 

 invertebrate host, of halteridium stages alternating with those 

 in which the trypanosome form is assumed. It is evident that 

 if this were substantiated important effects would follow in our 

 views as to the morphology not only of the trypanosome group, 

 but also of that to which the malarial parasites belong. 



Certain criticisms of these results have been made, especially by 

 Novy and MacNeal, who sought confirmatory evidence by means of their 

 culture method. These observers are of opinion that the appearances 

 described by Schaudinn were due to his dealing with a mixed infection 

 of the owls by trypanosomes on the one hand and haemamoebae of the 

 halteridium type on the other. They examined a very large number of 

 different species of birds, and established the fact that infection with 

 halteridium parasites on the one hand and with trypanosomes on the 

 other is extremely common, and further, that in the blood of the same 

 bird both halteridium and trypanosome infection could be observed. 

 The bird trypanosomes could be readily cultivated, and it was observed 

 that no cultures were obtainable from birds in which halteridia were 

 alone found, and further, that when a trypanosome isolated from a case 

 where both forms of parasite had been seen was injected into a fresh 



