Bacteria 
the case, the reason is because they have either ex- 
hausted all the food that they can get in the body or 
else have made it uninhabitable for themselves by their 
own poisonous excretions, These theories leave, how- 
ever, out of sight a very important side of the question. 
The cells in the animal’s body when a bacterial 
enemy invades it are not dead but alive, and invariably 
make some sort of effort to resist them, 
The only possible answer for such a live cell in an 
animal body is to fight a poisonous bacterial excretion 
by secreting something else. Such mysterious defensive 
secretions are called anti-bodies, and may either be 
antitoxins, which neutralise the toxins (that is, bacterial 
excretions), or they may be bactericidal bodies which 
kill the bacteria themselves. 
This response of live cells to bacterial enemies is 
another clear case of “fitting reactions.” 
We are obliged to mention here a rather disturbing 
and agitating fact with regard to our own bodies, but 
the reader must please consider it in a bright and hope- 
ful spirit. There are, wandering everywhere within our 
own bodies, multitudes of white blood corpuscles or 
phagocytes, whose duty it is to destroy and devour any 
objectionable microbes that have managed to enter us. 
We have no control over these phagocytes, who are 
entirely free and independent. 
When a foreign bacillus has entered our body, it 
begins to.give forth its poisonous excretions ; these pene- 
trate to and eventually reach a phagocyte. The whole of 
the latter’s protoplasm is at once on the alert ; stimulated 
and “anhungred” by the trace of this secretion, forth- 
with it proceeds, crawling as rapidly as possible, towards 
the bacillus until the supreme moment arrives in which 
it engulfs or enfolds the unfortunate microbe within its 
own jelly-like body and promptly digests it to death. 
56 
