Annual Address by the President. 
13 
seems to be some connection between it and the thyroid, because it is 
found that after extirpation of the thyroid the pituitary body increases 
in size. Also that complete thyroidectomy can be done without serious 
symptoms if the operation be performed in successive stages so as to 
allow the pituitary body to hypertrophy. Again, cases of myxoedema 
and sporadic cretinism are often associated with marked hypertrophy 
of the pituitary body. ( Lazar us-Barlow. ) 
The second part of this discourse deals with the “acquired defenses/' 
or the correlation of physiological processes brought about to meet ab- 
normal stimuli. Entailing, as it must, some description of the state 
known as immunity, it would be unwise to attempt more than a brief 
sketch of the problems concerned. 
Immunity is usually divided into three varieties, viz., (1) natural, 
(2) acquired, and (3) hereditary. Whichever of these is present, the 
tissues possess the power of repelling infection, either by destroying it 
completely or rendering it harmless through chemical combination. 
If it be a living organism, it is destroyed by one of two methods: 
(a) Either by the bactericidal properties of the blood serum or of the 
other body fluids (bacteriolysis) ; or (b) by the activity of the living- 
cells, which attack it, ingest it and digest it (phagocytosis). But, if on 
the, contrary the infection be a soluble toxin, then the process of ren- 
dering it harmless must be a purely chemical one. 
It will perhaps facilitate matters if we discuss the question under the 
above mentioned heads, and first investigate the processes by which the 
tissues resist the attacks of living micro-organisms. 
In studying the action of blood serum on micro-organisms, many 
curious facts have been discovered. It was naturally believed that fresh 
blood serum would form an excellent culture medium for most micro- 
organisms, which flourish at the expense of the human body. On the 
contrary, experiment demonstrated that fresh serum actually hindered 
and in some instances destroyed cultures of most organisms, whether 
pathogenic or non-pa thogenic. This property, which seems to be pos- 
sessed to a certain degree by most serums, gradually disappears as it 
ages, until eventually it forms as good a cultivating medium as any 
other albuminous compound of similar constitution. This germicidal 
property varies greatly with serums of different animals, and even with 
the serum of the same species of animals, but it is rarely absent. The 
same property is possessed to a certain extent by the other fluids of 
the body. Thus the peritoneal fluid possess it, and if a cultivation of 
attenuated typhoid bacilli be injected into the peritoneal cavity of a 
guinea pig it occasionally happens that the whole culture is destroyed, 
as it were, explosively, by the bactericidal action of the peritoneal fluid. 
