296 THE PROTOZOA 



corpuscles, and so pass into the general circulation. Within the corpuscle 

 they grow into the adult form, which is finally set free from the corpuscle as 

 a trypanosome of normal structure. The adult trypanosome (Fig. 128, a), 

 swimming freely in the blood-plasma, may either be taken up by the inverte- 

 brate host in which it develops, or may repeat the process of multiplication 

 by schizogony. 



The second type of multiplication was first described by Hartmann from 

 hyportrophied endothelial cells of the lung ; Chagas (426) has since found it 

 in the tissues of the body, more especially in the cardiac muscle, central nervous 

 system, and striped muscle. In this type the parasite is intracellular, and has 

 the appearance and structure of a Leishmania (cf. Fig. 138), a rounded 

 body containing a trophonucleus and a kinetonucleus, but no flagellum or 

 undulating membrane. 



On account of its power of multiplication by schizogony, Chagas has made 

 T. cruzi the type of a special genus, Schizotrypanum ; the type of multiplication 

 observed in the lung-capillaries is not essentially different, however, from that 

 of T. leioisi in the blood, except for its alleged sexual dimorphism ; and, accord- 

 ing to Carini (424), similar processes of schizogony occur in other trypanosomes. 

 The intracellular multiplication in the tissues, however, recalls strongly that 

 of the parasite of kala-azar (see p. 316, infra). Schizotrypanum thus forms 

 an important link between a typical blood-trypanosome, such as T. lewisi, 

 and a tissue-parasite, such as the species of Leishmania, in which the free 

 trypanosome-phase no longer exists, apparently. 



Chagas considers the multiplication of Schizotrypanum cruzi in the tissues as 

 non-sexual, and serving to increase the number of parasites in the host, but that 

 which takes place in the lung- capillaries as a process of gametogony whereby 

 the sexually differentiated adult forms are produced. His grounds for this 

 interpretation are, first, that in human blood the adult trypanosomes exhibit 

 a dimorphism rarely found in guinea-pigs infected artificially, in which also 

 schizogony in the lung is seldom observed ; secondly, that the invertebrate 

 -host, Conorhinus, is always rendered infective if fed directly on infected 

 human blood, but very rarely becomes infective if fed on guinea-pigs, even 

 when these animals show an intense infection. He suggests that the greater 

 resistance of the human organism to the parasite stimulates the production 

 of sexual forms which the trypanosome may cease to produce in a less resistant 

 host. 



In the more familiar pathogenic species, such as T. brucii, T. gambiense, 

 etc., the development in the vertebrate host takes the form mainly of continued 

 multiplication by binary fission simply. Reproduction of this kind may pro- 

 ceed until the trypanosomes swarm in the blood ; or, on the contrary, the 

 trypanosomes may be at all times relatively few in number, even when 

 fatal to their host. T. brucii, for example, may produce in different hosts 

 an acute or a chronic form of disease ; in the latter case the infected animal 

 may live a long time, and the parasite exhibits very limited powers of multi- 

 plication. The behaviour of the parasite in the natural hosts to which it is 

 harmless has not been studied. 



In many pathogenic species, periods of multiplicative activity, during 

 which the trypanosomes are abundant, alternate with periods during which 

 the parasites pass into a resting condition in the internal organs, and become 

 scarce or disappear in the general circulation. In this phase they are alleged 

 to lose their flagellum, diminish in size, and become small, rounded " latent 

 bodies," which, according to Moore and Breinl (484), have only a single nucleus ; 

 but according to Fantham they are Leishmania-like, with distinct tropho- 

 nucleus and kinetonucleus. From resting stages of this kind the active 

 trypanosomes are developed again. Laveran (462), however, denies that there 

 is a non- flagellated stage of development in the vertebrate host, and considers 

 that the elements described as "latent bodies" represent involution-stages of 

 the parasites that is to say, forms which have become deformed in structure 

 owing to unfavourable conditions, but not to such an extent as to be incapable 

 of recovery if the conditions improve. 



