1804] The Action of Leucocytes Toward Foreign Substances. 317 
of the substances is removed from the tissues. The balance of 
power continually wavers between these two hosts, on the one 
hand the leucocytes and on the other the different kinds of 
organisms and matter, injurious or non-injurious, to which the 
animal body is hourly exposed. If the invaders are too strong 
the results become evident in the sickness or perhaps death of 
the animal. But if the leucocytes are victorious, and are able 
to clear the system of the foreign substances, normal conditions 
are again established and with them the health of the individ- 
ual. By no means is it necessary, however, that the conflict 
become apparent externally. This at least is the story 
picturesquely put as the founder of the“ Phagocyte Theory A 
reads it. It may be rather extreme; certainly there are those 
who consider the protective part played by the leucocytes to be 
quite small, relatively speaking or merely incidental. That 
they can and do ingest foreign particles and are subsequently 
to be found in the various tissues bearing their loads, is how- 
ever, proved. Itis only the interpretations laid on the facts 
that differ. 
Many experiments have been made from a pathological 
standpoint to prove, if possible, the true part played by the 
various tissues and cells in diseases, which owe their existence 
to the presence of foreign matter or foreign organisms in the 
body. Naturally from the medical standpoint these exper- 
iments have been made on mammals of various kinds, the 
only other animal used being the- ever useful frog. In con- 
trast to this basis of work is the normal physiological condition 
existing under ordinary circumstances in animal life. All 
the experiments, of which the results are here given, were made 
under as purely normal conditions as possible, in every way 
anything that might produce abnormal results, being avoided. 
The animals used for these experiments were the two sala- 
manders, Necturus maculatus or the Mud-puppy and Orypto- 
branchus alleghaniensis, the Hell-bender. 
For several reasons these animals afford peculiar advant- 
ages for an investigation of this kind. Of great importance 
among these is the large size of the leucocytes and of the vari- 
ous tissue cells, and also the comparatively simple structure of 
