ON THE PHAGOCYTES OF THE ALIMENTARY CANAL. 481 
On the Phagocytes of the Alimentary Canal. 
By 
Armand Ruffer, M.A., M.D.(Oxon.,). 
With Plate XXXI. 
Durine the last few years our knowledge of the pathological 
appearances found in animals suffering from an infectious 
disease has, thanks to M. Metschnikoff’s labours, been con- 
siderably extended. Infectious diseases for some years past 
were known to be caused by the presence of pathogenic micro- 
organisms in the tissues of animals—each malady being due to 
a distinct specific germ—and most of these specific germs had 
been isolated and cultivated (e. g. typhoid fever, tuberculosis, 
pneumonia, diphtheria, &c.). Some of these organisms more- 
over, when inoculated into animals, gave rise to morbid 
symptoms and to pathological appearances similar to those 
seen when manis invaded by them; whilst others (e. g. typhoid 
bacillus) proved fatal to some species of animals only (e. g. 
mice), though the clinical aspect and post-mortem lesions 
when the typhoid bacilli were injected in mice did not in any 
way resemble those produced by the same bacilli when the 
human species was attacked by them. 
It was, however, soon noticed that some species of animals 
were able to resist the inoculation of even large numbers of 
some kinds of specific germs. Animals belonging to another 
species, on the other hand, suffered but little when few 
specific germs were injected into their system, but did when a 
larger number of the same germs was introduced. Clinical 
observations had already demonstrated the fact that when an 
