1891.] Wandering Cells in Animal Bodies. 521 
experiments bearing on the question. Many have confirmed the 
theory, but there are also those who bitterly oppose it, and among 
such there are a few very prominent scientists. 
Before saying anything about this other side of the question, it 
may be of interest to depart from the subject for a moment, and 
notice a few important facts in regard to the supposed micro- 
organisms of disease. 
Different species of bacteria—using the term to include all 
micro-organisms—appear everywhere in great numbers ; but they 
are not all to be dreaded as enemies of mankind. When an 
animal dies its body is disintegrated and returns to dust by their 
action. Not only is this the case, but some species are actually 
of great benefit to our living bodies, by helping to carry out the 
functions of some of its organs. Some time ago, however, the 
presence of certain specific microérganisms was noticed to be of 
constant occurrence in certain diseases, while they were absent in 
a normal condition. The discovery was an interesting one. 
Investigations multiplied, and finally a great number of diseases 
were believed, by some, to be caused by these so-called “ germs.” 
It made little difference whether or not there was any other 
reason for it than the presence of some form in the course of the 
disease, which was supposed to be its cause. Finally conservative 
men saw the danger of allowing this unsound reason of post hoc, 
ergo propter hoc, to carry things any farther. Better reasons for 
the prevailing belief were asked for, and generally failed to be 
given. Almost everything was then received with doubt, and 
to-day the pendulum of popular belief in the subject seems to 
have swung very far in the opposite direction. This is 
evidenced in a statement by Dr. Koch, the great German bacteri- 
ologist, who has recently created such an interest through the 
world by his supposed cure for consumption. Ina recent address 
before the International Medical Congress, he says that ssas — 
microdrganisms are positively proven to be the causes of disease : 
namely, those of anthrax, erysipelas, and tuberculosis. Other 
great authorities, however, would add a few more, such as those 
causing glanders, cholera, pneumonia, and so on. At any rate, 
the number is now surprisingly small. Variations of the theory 
