Notes on Toxoplasma gondii. 



73 



In size, as can be seen from the figures, they agree very closely with the 

 measurements given by Mcolle (5, p. 99) for the average parasite from the 

 gondi, namely, 5-5*5/* in length by 3-4/i in breadth. 



The nucleus is generally clearly visible as a rounded region, clearer than 

 the rest of the body and somewhere near its centre (figs. 9 and 10). Fig. 11 

 shows a dividing form with two nuclei. 



In some specimens definite round refringent granules are to be seen, some- 

 times only one as in fig. 9, but never in large numbers. These will be 

 referred to again later. 



In preparations stained by one of the exact cytological methods it can 

 easily be seen that the nucleus is of the protokaryon type, that is, it consists 

 of a sharply defined karyosome suspended in a clear vesicle (fig. 12). The 

 nucleus is probably bounded by a membrane, which is, however, in no case 

 distinct, and only occasionally is there any peripheral chromatin (fig. 13). 

 The karyosome, no doubt, encloses a centriole, since a centrodesmose is 

 formed during fission, as will be described later, but it has not been found 

 possible to differentiate the staining of the small karyosome in order to make 

 the centriole apparent. 



In the alveolar cytoplasm there are often fairly large vacuoles, and the 

 refringent granules seen in living specimens take up chromatin stains very 

 readily, and are probably, I think, of the nature of reserve chromatin, or 

 volutin, as described by Reichenow (6, pp. 328-331) for Hcemogrcgarina 

 stepanowi. In some cases they have almost exactly the size of the 

 karyosome, and since they may occur quite close to the nucleus (figs. 7, 14, 

 15, 17, and 22), they are apt to be somewhat confusing. 



The parasites generally lie in distinct vacuoles in the protoplasm of the 

 host-cell (figs. 3-5) ; the formation of these might possibly be attributed 

 to the reaction on the part of the cell by which it throws out some sort 

 of secretion round the parasite, as suggested by Eow (7, p. 749) in the 

 case of Leishmania tropica, but it seems more likely to indicate a destructive 

 liquefying action by the parasite on the protoplasm of the host-cell. This 

 latter explanation would account for the fact that cells infected with many 

 parasites are in an advanced state of necrosis. 



Free parasites may be of different sizes and are frequently found under- 

 going fission. Intracellular forms often appear to have divided repeatedly 

 in rapid succession, giving rise to forms which are much reduced in size 

 (fig. 4, s). Those nearer the boundary of the cell seem to break away at 

 intervals as shown in this figure, and all that is seen to remain of some 

 cells is a degenerating nucleus with a fringe of cytoplasm. 



