THE STRUGGLE FOR LIFE. 221 
surface, the battle has been in vain, fresh poisonous pro- 
ducts are formed in it, and these being absorbed by the 
iymphatics, are conveyed into the blood-stream, and the 
blood itself is poisoned by them. Again, if so many Bac- 
teria have found entrance, that there is an_ insufficient 
number of scavenger cells or phagocytes to cope with them, 
the defence breaks down, the Bacteria get past the police- 
men, and enter the general circulation, to find lodgement 
and multiply in the vulnerable tissues. And the same 
thing happens when the mass of dead tissue is too large for 
the number of white cells which can reach it. 
The remainder of my paper will refer almost exclusively 
to the Bacteria, the way in which they are injurious, and 
the methods by which the body is defended against them. 
It will be seen from what I have said, that the extent of 
the danger depends greatly on the number of invaders, 
and not only so, but also on their character, because some 
races of the same species are much more active and vir- 
ulent than others. This partly explains why some epidemics 
of the same disease are much more fatal than others, I say 
partly, because there is no doubt that the sanitary sur- 
roundings have a great influence on the power of the body 
to resist the poisons generated by them. I have omitted 
to say that, broadly speaking, all epidemics are produced 
by the entrance of poisonous Bacteria into the body, every 
contagious disease being caused by its own specific Bac- 
terium, and not only these, but also some other diseases, 
not usually called epidemic, such as tubercle. 
Bacteria, when they have effected a lodgement in the 
body, multiply, and do mischief in two ways: in one, by 
the local injury they do to the tissues themselves, and, in 
the other, by the production of a poisonous secretion to 
which the name of toxine has been given. This may be 
produced in such quantities as to directly destroy life before 
the defenders have time to oppose it. But in some way 
