486 ARMAND RUFFER. 
follicles more or less fused with one another, and situated with 
their main part in the submucosa, but extending with their 
summit to the epithelium of the free surface of the mucosa 
(Klein). They are covered by a single layer of columnar epi- 
thelium, which is invaded by, and more or less replaced by, the 
lymph corpuscles of the adenoid tissue of the follicles (Stohr).' 
Ribbert,” in 1885, noticed that by staining sections of the 
vermiform appendix by Gram’s method numerous micro- 
organisms could be demonstrated in their interior. He further 
made the remark that many of these micro-organisms stained 
badly and showed signs of degeneration. He attributed this 
change to the action of the leucocytes of the Peyer’s patches. 
Bizzozero® confirmed Ribbert’s researches in the same year, 
but thought that the cells containing micro-organisms were 
not ordinary leucocytes, as they appeared to be larger. 
Metschnikoff,* in 1877, examining the mucous covering of the 
surface of the tonsils, found in it numerous leucocytes crammed 
with micro-organisms. 
The tissues which I used for my investigations were always 
prepared in the following way. The animals (rabbits, dogs, 
guinea-pigs) had always been kept in the Institute for some 
days beforehand, and appeared to be perfectly healthy. None 
of them had ever been used before for any experiments what- 
ever. They were chloroformed to death, and as soon as they 
had ceased to breathe the tissues to be investigated were cut 
out and at once plunged into absolute alcohol, in which they 
were kept till properly hardened. 
After being soaked in chloroform, ether, and paraffin they 
were cut after long (forty-eight hours) immersion in the latter. 
I usually at once glued them to the cover-glass with a mixture 
of glycerine and albumin, removed the paraffin with benzine, 
and after washing them for five minutes in absolute alcohol, 
and for an equal period in water, stained them with alum- 
1 Stohr, see Heidenhain, ‘ Pfliiger’s Arch.,’ 1888. 
* Ribbert, ‘ Centrbl. f. Bakt.,’? 1885. 
3 Bizzozero, ‘ D. med. Wochenschr.,’ 1885. 
+ Metschnikoff, ‘ Ann. de |’ Iustitut Pasteur, No. 7, 1887. 
