1912.] The Development of a Leucocytozoon of Guinea-Pigs. 69 



room — the granules of the leucocytes begin to stain, after which their 

 nuclei gradually stain a deep blue ; the contours of the erythrocytes, as well 

 as those of the leucocytes, show up clearly, and the method is a pretty 

 example of in vitro staining. In some of the larger mononuclear cells the 

 colourless parasites will be noticed at one side of the protoplasm. These 

 parasites are inside the cell, because the shape of the nucleus of the 

 lymphocytes is moulded according to the size of the parasite, which grows 

 larger as it develops — in its youngest stages it is small, while in its last 

 intracellular stages it bulges the lymphocyte cell wall and squeezes the 

 nucleus into a small space ; this point is of interest because, as Hunter has 

 shown, Patella claimed that Kurloff's bodies lie upon and not in the 

 lymphocytes. In cells containing the larger parasites smaller vacuoles can 

 also be seen ; these latter always remain clear and transparent even when 

 examined on stain-containing jellies, and they vary in numbers, and slightly 

 in size, in different examples. It has been suggested that these smaller, 

 subsidiary vacuoles are polar bodies, but more probably they contain 

 excretory products of the lymphocytozoa into the cytoplasm of their hosts, 

 for they become larger and more numerous as the parasite grows. 



When examined on the jelly, and immediately before the staining of the 

 nucleus of the leucocytes, the contents of the parasites begin to stain* — the 

 internal chromatin structure of the spherical sac embedded in the lympho- 

 cytes' cytoplasm becomes purple and remains stained for several hours, so 

 that its examination is readily made. If the bloods of a number of infected 

 guinea-pigs are watched in this manner from day to day what appear to be 

 the successive stages of the growth of the parasite in the lymphocyte can be 

 seen and drawn ; but the leucocytes of a single animal at any particular 

 moment contain, usually but not always, parasites in the same stage of 

 development. The cycle, however, can be followed by observing the blood 

 of one guinea-pig hourly. 



The interpretation which I place upon the appearances I have seen are as 

 follows : — The parasite presents itself, in the smallest phase of its intra- 

 corpuscular cycle, as a tiny translucent body embedded within the cytoplasm 

 of the larger mononuclear blood corpuscles and near the periphery of those 

 cells. Usually one of such bodies is present in any one cell, but occasionally 



* It must be emphasised that if the jelly contains excess of salts or impure stains, the 

 wall of the parasite will stain in an irregular manner, and then patches of stain will hide 

 its contents. Furthermore, if the blood on the jelly dries, or if the blood is fixed in any 

 way, the same thing occurs. Similarly, patchy staining is obtained by the various fixed 

 film methods in vogue, as, for example, Eomanowsky's or Jenner's stains. Even Azur 

 stain, when applied to the dried or fixed films of blood, will not demonstrate the details 

 of the development of the parasite. No alkali should be added to the jelly. 



