130 Proceedings of the Royal Physical Society. 
say that it is quite unsafe to make a general deduction from 
one instance, however marked it may be, and that it is 
unlikely we shall find results at all corresponding to those 
obtained with thyroid. Still, the possibilities have an allur- 
ing effect upon the imagination, and in connection with the 
use of animal extracts it may not be uninteresting to refer 
to some of its. historical associations. In ancient Egypt 
human brains were prescribed for eye diseases. In the 
Talmud, a dog’s liver is permitted for the bite of a mad dog. 
In China, at the present time, a decoction of scorpions is 
used in fever, rat’s flesh is eaten as a hair restorer, and 
leprosy is supposed to be curable by drinking the blood of a 
healthy infant. Amongst cannibals, you will remember that 
eating the heart of a warrior is believed to give courage. 
These might be multiplied indefinitely, but they are sufficient 
to show that in unenlightened time there was a belief in the 
remedial efficacy of the organs or tissues of human or animal 
bodies. 
I next desire to lay before you facts which have been 
discovered in the investigation of diseases due to bacteria, 
and at the same time to refer to light which has in this way 
been thrown upon biological processes. On this subject I 
have to ask your patience, for it is necessary to enter into 
considerable detail. 
It has long been known that the blood taken from a 
person suffering from certain infective diseases could com- 
municate the disease when introduced into the body of 
another person; but there was no attempt to distinguish 
which of the elements in the blood was the carrier of the 
infection. It had, for instance, been shown in the case of 
the calf that the transfusion of blood, or of lymph taken 
from an animal at a certain stage of vaccine eruption, con- 
ferred immunity on another animal. This was looked upon 
as an indication of the virulence of the blood, and as a proof 
that the blood contained the special morbific agent. The 
blood-serum was looked upon as occupying quite a secondary 
place, and as performing an almost purely physical or passive 
function—as, in fact, an inert vehicle. 
This idea, which was the predominant one, has gradually 
