GENERAL BACTERIOLOGY 
75 
phagocytosis of Metchnikoff—a phenomenon which 
doubtless plays a tremendously important part in many 
infections. 
On the other hand, Metchnikoff’s theory of 
phagocytosis does not explain as many of the phe¬ 
nomena of immunity, as does Ehrlich's, and it is neces¬ 
sary to use both theories in order to have a clear pic¬ 
ture of immunity. 
3. D ’Herelle’s Phenomenon of Bacteriophage.—As a 
result of extensive experimental studies D ’Herelle of 
Pasteur Institute claims that he discovered an ultra- 
microscopic organism (one which cannot be seen with 
an ordinary microscope), which he claims is the main 
source of our immunity. According to him, this ultra- 
microscopic organism or, as he calls it, bacteriophage, 
is parasitic upon (that is, lives at the expense of) ordi¬ 
nary bacteria (just as bacteria are parasites upon human 
body), and during the disease development destroys the 
bacteria which produces the given disease; he demon¬ 
strated the presence of bacteriophage by mixing a part 
of dysenteric stool with the dysentery culture where¬ 
upon in the latter bacteriolysis took place, and the bac¬ 
teriolytic substance could then be transmitted and trans¬ 
ferred from this tube to others. D’Herelle’s idea, there¬ 
fore, is that in all infectious diseases the question of 
recovery depends upon the fact that in the human and 
animal intestines there are the minute (ultramicro- 
scopic) bacteria which get into the disease producing 
bacteria and secrete a dissolving (lytic) substance on 
these bacteria, and then recovery takes place; there are 
bacteriophages for all bacteria. 
In D’Herelle’s monograph just published under the 
title “The Bacteriophage” evidences are given where 
the administration of the properly produced bacterio- 
