ON THE PHAGOCYTES OF THE ALIMENTARY CANAL. 491 
such nuclei, micro-organisms healthy and digested, &c. (see 
further on). 
The lymphocytes in the Peyer’s patches have been described 
as small mono- or poly-nucleated cells, with nuclei staining 
uniformly and deeply with carmine. The nuclei are surrounded 
by a small amount of protoplasm of a pale rose colour. More 
careful examination, however, of the lymphoid tissue reveals 
the presence of other mononucleated lymphocytes, differing 
only slightly at first from the other cells surrounding them. 
The nucleus of these cells is somewhat paler and its reticulum 
slightly more apparent, though the protoplasm may not be at 
all increased in size as yet (see fig. 1). Other cells possess a 
nucleus which is again slightly larger, paler, and more vesi- 
cular than the latter, as if the nuclear juice had increased at 
the expense of the solid part of the nucleus (see fig. 2). 
It would be very easy to mistake these structures, represent- 
ing the initial stages of the formation of macrophages, for 
ordinary leucocytes. The nucleus of others shows a further 
augmentation, becoming more oval and more like a vesicle in 
shape (see figs. 3, 4), whilst the protoplasm surrounding it also 
becomes more abundant (see figs. 5, 6), the whole cell becoming 
larger. Lastly, the nucleus and protoplasm become enormous 
(see figs. 7, 8, 8 bts), and the macrophage is formed. All the 
stages in the development of the macrophage may thus be fol- 
lowed in the Peyer’s patch. The macrophage is merely a 
lymphocyte which has assumed a new shape, and, as we shall 
see, a new function. These cells greatly resemble those found 
by Heidenhain! in the villi of the guinea-pig. True macro- 
phages are not present as a rule in the rabbit’s villi, but they 
are found in great numbers in the Peyer’s patches, as well as 
in the tonsils of many animals. 
The macrophages are not scattered in the same numbers 
throughout the whole Peyer’s patch. They certainly do ad- 
vance right up to the attached border of the epithelial cells, 
but the superior layers do not contain them in great numbers, 
few only, two to five, being seen in one field of the microscope. 
1 Heidenhain, loe. cit, 
