Vice-President’s Address. 131 
had to give way, as a result of investigations into disease 
processes. 
Perhaps the first new power which blood-serum was found 
to possess was the destructive action which it sometimes 
exercised on certain micro-organisms, and which has become 
known as its bactericide power. It was found that the 
serum of certain animals opposed the development of certain 
micro-organisms, and even destroyed them, so that no culture 
of them could be obtained from a mixture of the serum and 
the microbe. Some of the instances in which this bactericide 
property was present in the serum occurred in animals which 
were refractory to the action of certain microbes and the 
disease which they produced. At first it was thought that 
this bactericide property might largely account for the 
immunity which some animals enjoyed towards some 
diseases, and that the effect might be regarded as the result 
of a chemical action exerted by the serum upon the microbe. 
This was, however, soon discovered not to be a general law, 
but rather an exception to a more general law, and to which 
fuller reference will be made hereafter. That this bactericide 
power is not a simple physical phenomenon, but is rather 
biological or vital in its nature, is supported by the fact that 
a moderate degree of heat destroys it, while it in no way 
modifies the other physical or chemical properties of the 
serum. It was natural that efforts should be made to dis- 
cover a special substance on which this bactericide power 
depended, and various substances, known as defensive pro- 
teids, globulins, or alexines, or as diastatic in nature, have 
been described by various investigators, although their results 
can hardly be regarded as accepted or conclusive. 
Other experiments have shown that, in certain cases, the 
blood-serum taken from an animal refractory to a certain 
microbe formed a medium in which the microbe could be 
successfully grown, thus tending to show that the influence 
was not the result of a simple microbicide power. In some 
cases, however, the interesting fact was revealed that a 
microbe grown in such serum lost, in some instances, its 
special pathogenic influence, whilst in other instances the 
reverse of this occurred. From these latter observations it 
