484. ARMAND RUFFER. 
animal be not vaccinated or does not normally possess a certain 
amount of resistance to pathogenic micro-organisms, its cells 
do not try to destroy these fungi, or, if they do make any 
attempts, they only absorb and digest very few of them. The 
parasites then multiply and kill the animal, partly by producing 
mechanical lesions, but mostly by poisoning it with the toxic 
substances they secrete. Vaccination against a contagious dis- 
order, therefore, confers on these macrophages and microphages 
the power of destroying the specific organisms causing the 
disease. 
Now, in the alimentary tract various pathogenic organisms 
are frequently present. Indeed, some of them are constantly 
found there, even in healthy animals. There are few adult 
men who, at some time or other, have not swallowed the bacilli 
of typhoid fever or tuberculosis, though most have experienced 
no evil effects of them. The bacilli of diphtheria and pneu- 
monia have been met with in the mouths of healthy subjects, 
who had never contracted these diseases. The septic vibrio of 
Pasteur is always present in the intestine of the rabbit, though 
unable to get through the walls of the gut. How is it, then, 
that the micro-organisms do not pass into the blood or 
lymphatics ? 
In order to throw light on this question it was necessary to 
see what takes place in the healthy animal, and to observe 
whether the numerous micro-organisms, normally present in 
the alimentary tract, make any efforts to force their way 
through the walls. It is well known that many of the infec- 
tious processes affecting the intestinal tract originate in the 
lymphoid tissues, namely, in the tonsils and Peyer’s patches, and 
accordingly the first investigations concerning the penetration 
of micro-organisms through the intestinal walls have been made 
on the Peyer’s patches (Ribbert and Bizzozero). 
In this paper I shall only speak of the phagocytic processes 
taking place in the lymphoid tissues of the alimentary tract of 
healthy animals, pointing out afterwards how these facts throw 
some light on pathological observations. I must reserve for 
another opportunity an account of investigations as to the fate 
