August 4. 19 10] 



NATURE 



1 4': 



It-Misi of rats, is that in the latter the fiagellum is 

 retained, as a rule, and in the former is always 

 lost, during the process. In 5. criizi there appears 

 to be an alternation between periods of multiplication 

 with schizogony in the lungs, with adult free trypano- 

 somes occurring sparingly in the blood, and periods 

 in which the peripheral blood contains numerous try- 

 panosomes. In the case o' experimental animals, it 

 was found, as a rule, th-^t at the time of death 

 trypanosomes were very scanty in the blood, while 

 schizogony was proceeding actively in the lung. 



The trypanosome, when about to undergo multi- 

 plication, first throws off the fiagellum and undulating 

 membrane; it may or may not lose its kinetonucleus 

 at the same time. It then curls up (Fig. 2, /)), and 

 contracts into a rounded mass, the schizont (Fig. 2, 

 c), after which the trophonucleus and the kineto- 

 nucleus, also, if present, divide each three times to 

 form eight small nuclei of one or both kinds (Fig. 2, 

 d). The protoplasmic body then divides up within its 

 own skin (periplast) into as many parts, termed by 

 Chagas merozoites (Fig. 2, e). Each merozoite con- 

 tains either a single trophonucleus, or a kinetonucleus 

 in addition. The generation with a persistent kineto- 

 nucleus is regarded bv Chagas as male, that without 



;« "^ 





Fio, 2 —a-i, Phases of Schizotrypanum crusi in vertebrate 

 blnod a, the two fortn^ of the adult trypano-oms, " male " 

 (upper) and "iern,le" (lo*crl, from human blood;'*, pre- 

 parations for schizogony; c, rchizont ; tt, divisio of the 

 nucleus of the schizont ; €, division of the schizo.tt into eight 

 merozoites ;y; merozoite in a blood-corpuscle ;^, inira-corpns- 

 cular ph^^ein late stage of growth ; h, similar phase escaping 

 from the cor luscle, the fla<ellum n rt yet f.rmed ; i, similar 

 phase, the Hagellum in process of formation. 



any such body as female. Although the author in- 

 sists on interpreting these and other differences as 

 sexual, it should be noted that no sexual behaviour 

 has been observed in any part of the life-cycle of the 

 parasite. 



The tiny merozoites are stated to escape singly from 

 their envelope and to penetrate into red blood- 

 corpuscles (Fig. 2, /), in which they grow into the 

 adult form (Fig. 2, g, h). In those merozoites which 

 are without a kinetonucleus, this body arises by divi- 

 sion of the single nucleus present. The fiagellum 

 and undulating membrance appear to be formed when 

 the organism is full-grown, sometimes not until it has 

 escaped from the blood-corpuscle (Fig. 2, h, i). It is 

 remarkable, however, that Chagas does not figure any 

 Intracorpuscular phases intermediate in size between 

 the very smallest and -those which are practicallv full- 

 grown ; and it must be said that many of his figures 

 of the later growth-phases are not at all convincing 

 as to the parasite being really within the corpuscle. 



NO. 2127, VOL. 84] 



With completion of growth and liberation from the 

 corpuscle, the adult phase of the free trypanosome is 

 reached. 



On the ground that Schizotrypanum cruzi differs 

 from all known trypanosomes in undergoing multipli- 

 cation by schizogony, and in the possession of an 

 intracorpuscular phase, Chagas regards it as a form 

 connecting the trypanosomes and the Hsemosporidia 

 (malarial parasites and allied forms), and supporting 

 the union of these two groups in systematic classifica- 

 tion. This view raises questions which cannot be 

 discussed in a brief space. 



By experiments on the transmission, Chagas found 

 convincing evidence that the parasite goes through a 

 developmental cycle, with a minimum duration of 

 eight days, in the bug. Until this cycle is complete 

 the bug is not infective. It is a point of great in- 

 terest that, while bugs collected in human dwellings 

 and bugs fed in the laboratory on infected marmosets 

 transmitted the infection, he was never able to render 

 bugs infective by feeding them on infected guinea- 

 pigs. Chagas is of opinion that a certain condition 

 of the parasite is necessary to produce infectivity in 

 the bug, and that the requisite conditions are furnished 

 by the blood of human beings or marmosets, but not 

 by that of guinea-pigs. Experiments to prove trans- 

 mission of the parasite through the egg of the bug 

 gave entirely negative results in all cases. 



Phases in the development of Schizotrypanum cruzi 

 in the invertebrate host are described by Chagas from 

 bugs bred in the laboratory and fed on infected 

 animals. The parasites begin to undergo a change 

 in the stomach of the bug about six hours after feed- 

 ing (Fig. 3, a, b, c) ; they lose their fiagellum and 

 contract into rounded forms which multiply actively 

 by fission (Fig. 3, d). After a period of multiplica- 

 tion, the rounded forms become pear-shaped, and 

 develop a fiagellum at the pointed end (Fig. 3, e, /); 

 thus are produced flagellates of the Crithidia type 

 (Fig. 3, g, h), which pass on from the stomach into 

 the intestine, and there multiply rapidly by fission. 

 As a result, the intestine becomes peopled by a swarm 

 of crithidial forms, the characteristic condition of the 

 infected bug. In a few instances Chagas found try- 

 panosome-like flagellates in the body-cavity and the 

 salivary glands (Fig. 3, ;'), and he regards these try- 

 paniform individuals as the last phase in the develop- 

 ment of the parasite in the bug, that is to say, as 

 the form in which the parasite is inoculated into the 

 vertebrates bv the invertebrate host. 



It should be noted here that the three principal 

 forms which the parasite assumes in the bug, namely 

 the rounded, crithidial, and trypaniform types, are 

 found by Chagas to occur also in artificial cultures 

 on blood-agar, and to succeed each other in the same 

 order. This parallelism indicates that these forms 

 represent the natural developmental cycle of the para- 

 site in the invertebrate host ; that the rounded and 

 especially the crithidial forms represent the multipli- 

 cative phase whereby the parasite establishes itself in 

 the bug, while the trypaniform individuals represent 

 the propagative phase destined to infect new hosts. 

 Chagas, however, interprets the facts observed in a 

 different manner. He regards the crithidial forms as 

 the end-product of an atavistic degeneration of the 

 parasite, a mere culture-phase which does not develop 

 further, and is of no importance for the transmission 

 to the vertebrate host and the continued propagation 

 of the parasite. On the other hand, he attaches great 

 importance to two forms observed by him in the bug 

 but not found in the artificial cultures, namely, en- 

 capsuled forms (Fig. 3, ;), which he believes to repre- 

 sent zygotes, although no conjugation has been 

 observed, and certain forms which he interprets as 



