D. Ward Cutler 
133 
whose walls ultimately fuse, leaving the food particle in the interior of the 
body. On reaching the endoplasm no change is observed for a period of time 
varying from 5 to 20 minutes, the longer period occurring when a relatively 
large body, such as a blood corpuscle, is undergoing digestion. Eventually, 
however, there is developed round the food a clear space, giving a very marked 
alkaline reaction to neutral red. Until this reaction sets in the food has 
apparently suffered no change except for the escape of haemoglobin, but soon 
after the onset of alkalinity the size of the food body diminishes until only a 
small portion remains, which is probably extruded from the cytoplasm. 
Many observers have studied the process of digestion in Protozoa: 
Nirenstein (1905) found in Infusoria that there were two periods, firstly an 
acid one followed in a short time by an alkaline one. In Actinospliaerinm , 
however, Greenwood (1894) found the acid period was omitted. 
In E. histolytica the endoplasm normally has an acid reaction, as shown 
by the effect of neutral red. It is possible, therefore, that the part of digestion, 
performed during the acid period in the Infusoria, occurs in E. histolytica 
during the interval that elapses before the onset of alkalinity. It may well 
be that in Actinosphaerium also the endoplasm is normally of an acid nature. 
MORPHOLOGY AND NUCLEAR DIVISION. 
The average size of E. histolytica is usually given as 25-30/x, though 
Hartmann considers that 15-20/x is the most common size. Dimensions, 
however, are of no value for the determination of species, as there is a wide 
range. For instance I have found forms measuring only 13/x which were 
undoubtedly E. histolytica , together with other amoebae which were 30-35/z 
in diameter. These measurements are certainly extremes, but size variability 
is as characteristic of E. histolytica as of other Protozoa. 
The resting nucleus is usually round or oval in shape and invisible in the 
living condition. Stained preparations show a fairly thin membrane on which 
chromatin is situated in the form of a thin layer. In the centre there is a 
karyosome, from which fine threads radiate to the periphery, and on these 
threads chromatin granules are usually found, Plate VII, fig. 5. 
The karyosome appears as an evenly stained matrix, but occasionally 
chromatin granules are found distributed through it. 
From the staining reactions and also from the subsequent history I con¬ 
clude that this central body is composed of both plastin and chromatin. 
This form of nucleus is typical for E. histolytica , when it is in the trophozoic 
condition. 
The changes which precede division are characteristic. The karyosome 
loses its compact form, becoming differentiated into chromatin granules and 
an homogeneous mass, composed almost entirely of plastin, Plate VII, fig. 6. 
Often the central plastin body is surrounded by a clear zone bounded by 
granules from which threads pass to the periphery, Plate VII, figs. 1, 9. The 
disposition of the granules, however, is quite indiscriminate, sometimes they 
