68 



Miss H. L. M. Pixell. 



Course of the Infection in Mice and the Distribution of the Pa/rasite in the 



Tissues. 



Mice are very susceptible to the effects of the parasites, which prove fatal 

 in from 5 to 15 days after intraperitoneal inoculation. The symptoms are : 

 (1) an increased rate of respiration until the last 12 hours or so, when 

 breathing becomes slow and laboured ; (2) a general loss of the senses, 

 especially sight — the mice appearing to be blind for the last day or two ; 

 (3) general lethargy — food, however, is taken in many cases almost as usual 

 until nearly the end. 



The individuals showed many post-mortem differences, which will be con- 

 sidered under the different tissues. 



(1) Peritoneal Fluid. — In some cases the peritoneal cavity is full of a 

 viscid, slightly cloudy fluid containing numerous parasites, both free and 

 intracellular — in Mice C and D (see below) this was the case and these two 

 were undoubtedly the best infected specimens — Mouse F, however, which had 

 an equally large amount of fluid, seemed to have nothing like the number of 

 parasites, not more, in fact, than A, in which there was hardly any peritoneal 

 fluid. It will be noticed, too, that in both A and F the course of infection 

 lasted seven days. 



Other anomalous cases will be noticed among the results of experiments 

 tabulated below, from which it would seem that the quantity of peritoneal 

 fluid cannot always be correlated with the number of parasites present, nor 

 is the rapidity with which they prove lethal necessarily proportional to their 

 number. On the other hand D had, perhaps, the best infection, and it was 

 the most rapidly fatal, whereas B, in which the disease lasted 12 days, was 

 found on post-mortem examination to have only a very poor infection. 



The parasites in well infected animals are to be found in numbers both 

 free in the fluid and enclosed in the cells floating in it. Of the leucocytes they 

 are nearly always mononuclears (Plate 9, fig. 1) that are affected ; only occa- 

 sionally has a polymorphonuclear been found to contain one or two parasites. 

 In other cases the parasites are embedded in, or attached to, cellular debris 

 (figs. 2, a-c) ; the origin of these masses of debris is sometimes difficult to 

 determine — they are referred to by Mcolle (5, p. 98) as " gangues." Still 

 more numerous, however, are the parasites in endothelial cells (macrophages) 

 which have evidently become detached from the peritoneum and float freely 

 in the fluid (figs. 3 and 4). 



(2) Mesenteries. — Finding that detached endothelial cells were so often 

 infected with parasites, I was led to examine the mesenteries themselves, 

 with the result that the endothelial cells forming these serous membranes 

 were foimd in many cases to be packed with parasites (figs. 5 and 6). 



