32 PRESIDENT’S ADDRESS. 
exact chemical nature has been somewhat better elucidated it will 
probably not be difficult to obtain others in the same way. 
From the above it is clear that not only is a co-ordination through 
the nervous system necessary in order that life shall be maintained in a 
normal condition, but a chemical co-ordination is no less essential. 
These may be independent of one another; but on the other hand they 
may react upon one another. For it can be shown that the production 
of some at least of the hormones is under the influence of the nervous 
system (Biedl, Asher, Elliott); whilst, as we have seen, some of the 
functions of the nervous system are dependent upon hormones. 
Time will not permit me to refer in any but the briefest manner 
to the protective mechanisms which the cell aggregate has evolved 
for its defence against disease, especially disease produced 
teeta: by parasitic micro-organisms. These, which belong with 
mechanisms. few exceptions to the Protista, are without doubt the 
Toxins and = most formidable enemies which the multicellular Meta- 
antitoxins. ; : : ; 
zoa, to which all the higher animal organisms belong, 
have to contend against. To such micro-organisms are due inter 
alia all diseases which are liable to become epidemic, such as anthrax 
and rinderpest in cattle, distemper in dogs and cats, small-pox, scarlet 
fever, measles, and sleeping sickness in man. The advances of modern 
medicine have shown that the symptoms of these diseases—the disturb- 
ances of nutrition, the temperature, the lassitude or excitement, and 
other nervous disturbances—are the effects of chemical poisons 
(toxins) produced by the micro-organisms and acting deleteriously 
upon the tissues of the body. The tissues, on the other hand, 
endeavour to counteract these effects by producing other chemical 
substances destructive to the micro-organisms or antagonistic 
to their action: these are known as anti-bodies. Sometimes the 
protection takes the form of a subtle alteration in the living 
substance of the cells which renders them for a long time, 
or even permanently, insusceptible (immune) to the action of the 
poison. Sometimes certain cells of the body, such as the white 
corpuscles of the blood, eat the invading micro-organisms and destroy 
them bodily by the action of chemical agents within their protoplasm. 
The result of an illness thus depends upon the result of the struggle 
between these opposing forces—the micro-organisms on the one hand 
and the cells of the body on the other—both of which fight with 
chemical weapons. If the cells of the body do not succeed in destroy- 
ing the invading organisms it is certain that the invaders will in the 
long run destroy them, for in this combat no quarter is given. For- 
tunately we have been able, by the aid of animal experimentation, 
to acquire some knowledge of the manner in which we are attacked 
by micro-organisms and of the methods which the cells of our body 
