H. W. Acton and W. F. Harvey 
263 
In one of oiir experiments, a virus obtained from a man’s brain was 
inoculated subdurally into two monkeys, two goats, a cow-calf, a rabbit, 
a guinea-pig and intramuscularly into a white mouse. The latter 
survived, but all the other animals died of rabies and showed the Negri 
bodies particular to the species. An emulsion of the brain of the rabid 
calf was inoculated subdurally into a rabbit. Large Negri bodies had 
been found in the cow-calf (PI. XI, figs. 3, 4). When the rabbit died 
the typical small Negri bodies of that animal were seen (PI. XI, 
figs. 5, 6). The incubation-period did not differ significantly in the 
rabbit and calf, for death took place on the IQth and 15^/t day re¬ 
spectively—that is to say we may assume the Negri bodies in each to be 
of about the same age. This experiment, together with our other 
observations, would indicate that the size etc. of the Negri body do 
not depend upon the virus, but rather on the kind of animal. This 
points to a dependence of formation on the response of the nerve cell. 
In fact we may go further and say that we are now able, for the above 
animals, to diagnose in an unknown section the particular mammal 
concerned by such characters alone as the size, shape, vacuolation and 
staining reaction of the Negri body. Moreover there appears to be 
some association between the size of the cell and the size of the Negri 
body. The above facts are not in accordance with conceptions of the 
parasitic nature of these bodies. If they were parasites we should 
expect them to be uniform in structure etc., whatever the animal which 
acted as host. Moreover they cannot be specific parasites and yet be 
found in other diseases than rabies. The denial of their parasitic 
nature does not affect the question of their importance for the diagnosis 
of rabies—a fact which has been amply proved. It still remains to be 
explained what these bodies really are. We consider that the nucleolus 
plays a large part in the formation of Negri bodies and therefore a 
consideration of the structure and variations of the nucleolus will not be 
out of place here. 
If we study the nucleolus of a normal ganglion cell of the central 
nervous system, we will find that it consists of a large single spherical 
body, which apparently is suspended in the nuclear network and shows 
no differentiation of structure. It is not composed of chromatin proper, 
and stains usually an intense black with the iron haematoxylin method 
of Mallory and a brilliant red by the methyl-blue eosin method of Mann. 
The peripheral portion is probably of a different composition to the 
fluid centre, and hence often stains a deeper black than the centre and 
so the bull’s eye effect which was first described by Heidenhaiu (1882) 
