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Prof. H. G. Plimmer. 



and delicate, and sometimes contains vacuoles. They are, on this account, 

 difficult to fix satisfactorily. I have found that fixation hy the vapour of 

 iodine dissolved in chloroform, as described by me in ' Koy. Soc. Proc.,' B, 

 vol. 86, p. 389, gave the best results. The nucleus consists, in what may 

 be regarded as a normal parasite, of a round dot or karyosome, which, before 

 division of the cell, lengthens and becomes rod-shaped and then dumb-bell- 

 shaped. Barely, a ring form of nucleus may be found, as in Plate 9, fig. 6. 



In many of the organisms the nucleus is either broken up into granules, 

 or the cell gets filled with granules which take chromatin stains (haema- 

 toxylin, fuchsin, thionin, have been those used), so that they are indis- 

 tinguishable from the nucleus. These granules may be the so-called 

 " infective granules," such as have been described by the late Major W. B. 

 Fry and Captain Banken, V.C. (3), in Trypanosomes, which the late Prof. 

 Minchin (4) acknowledged in the last paper written by him ; for the amount 

 of ordinary division seen does not seem to correspond with the enormous 

 number of parasites found in individual leucocytes. They have none of 

 them the reaction, with iodine fixation, of the reserve food granules seen in 

 Trypanosomes. 



The varieties of Toxoplasma I have found in a fossa, a fruit pigeon, and a 

 Say's snake, showed no motility when examined fresh, even on the warm 

 stage, neither did I observe any changes of shape. 



As regards size, the organisms vary too much in the same animal for 

 very approximate measurements to be of much use. In the fossa they were 

 the smallest, and varied from 2 /a to 8 p in straight length from end to end, 

 and from 1*4 /m to 2*5 fi in breadth at middle. In the fruit pigeon the length 

 varied from 3 /a to 8 /a, and the breadth from 2 /a to 5 /a. Those found in 

 Say's snake were larger, and varied from 7 fi to 10 /a in length, and from 

 3 ft to 6 fj. in breadth. These measurements were made on fresh, unfixed 

 organisms. 



In all these cases the Toxoplasmas were found free in the blood, but 

 in very small numbers ; they were generally found in the large mononuclear 

 leucocytes from the affected organs, often occurring in enormous numbers. 

 They were found principally in the lungs and pleural effusion and in the 

 bone-marrow in the fossa ; in the lungs and exudation from the lungs in the 

 fruit pigeon, and in the liver in Say's snake. None were found in the bone- 

 marrow of the bird or snake. The infected leucocytes show but little 

 alteration in the early stages of the infection, when they contain only 

 one or two parasites, but as these multiply the leucocyte enlarges enormously, 

 and the protoplasm becomes extremely thin and frothy in texture, and 

 there is always a marked hyperchromatosis of the nucleus ; the cell eventually 



