132 PROTOZOA AND DISEASE 



present, would attain full development : this I term the fully developed 

 lesion. 1 



The fully developed lesion thus defined presents an appearance 

 (Fig. 52) which differs markedly from either of the earlier stages. 

 Even in the naked-eye preparation (Fig. 49 ; 2) the tissue is seen to 

 be less opaque. Under the microscope this translucency is seen to 

 be due to a more open structure ; the intercellular spaces are wider 

 and the capillaries farther apart. Some of the latter are interrupted, 

 as shown in Fig. 52. 



There is no crowding of leucocytes within or around the capillary 

 walls ; thus the process is not that of ordinary inflammation. The 

 most striking feature is the presence of cells containing groups of 

 included cells e.g., Fig. 52; 7, and 7 1 ; and Fig. 53; 16. Some of 

 these cell-inclusions are nucleated, others not. A close examination 

 shows that they are not the ordinary leucocytes (such as are seen in 

 Fig. 53 ; 77) incepted by the tumour-cells. Some of them are under- 

 going mitotic subdivision. 



The nucleus of the majority of the cells that contain these bodies 

 consists simply of a nuclear membrane ; in a few, however, there is 

 an intranuclear body and network (Fig. 53 ; 26) ; such may be 

 explained by a parasite having entered the cytoplasm from another 

 cell. 



As in the earlier stages, so in these fally developed lesions, there 

 are numerous free cells undergoing mitosis. In a few instances 

 these mitoses may belong to granulation tissue cells in mitosis 

 (Fig- 53 ' 7# and 7P), but it is not possible to refer the bulk of them to 

 this source. The following points can be definitely established : 



i. Some of the cells in this area are surrounded by a definite 

 doubly refracting capsule (Fig. 53 ; 25}. 



1 This fully developed stage of the lesion has not, as far as I am aware, been 

 described before. This fact decided me in including some notice of this disease of 

 dogs in this volume. A comparison of Figs. 51 and 52 will serve to show how 

 marked are the objective characters that distinguish the tissue at the moment when 

 retrogressive change sets in ; but no mere drawing can give a full idea of the 

 highly refracting capsules and other peculiar features that this area presents. The 

 appearances are in marked contrast with any that are seen in lesions caused by 

 any bacteria with which I am acquainted. 



