800 
PROCEEDINGS OF SECTION I. 
immune to one of these diseases be mixed with a virulent culture it 
neutralises its pathogenic power so that it is no longer fatal to 
susceptible animals. They have also shown that the serum of an 
animal immunised against one or the other of these diseases is a thera- 
peutic agent of the greatest practical value. For obvious reasons it 
has been more successful in the case of diphtheria than of tetanus, 
since the existence of the latter disease cannot be diagnosed till the 
occurrence of muscular spasms, which are in themselves evidence of 
profound poisoning ; whereas in diphtheria the false membrane gives 
warning of the nature of the affection before any considerable quantity 
of the diphtheritic toxine has been absorbed. And in these early cases 
of diphtheria the treatment by antitoxic serum has been eminently 
successful. Every week the medical journals contain accounts of cases 
treated by this method with very encouraging results ; and in the 
hands of Professor Roux in Paris and of Arnson at Berlin it has 
lowered the death-rate of all cases of true diphtheria to the extent of 
some 30 per cent. 
Other investigators have established the fact that immunity may 
in like manner be produced to various other diseases by injecting into 
susceptible animals the filtered products (toxines) of the specific 
microbes, and that the blood serum of animals so treated is able to save 
others not so protected when inoculated with virulent cultures. 
.Demonstrations of this kind have been made with respect to the 
Diplococcus 'pneumonia , the bacillus of hog cholera, and the Vibrio 
Metschnikovi , 
It is particularly interesting to note that this antidote-producing 
power of the animal organism is not confined to the elaboration of 
antitoxines in response to the toxines of pathogenic bacteria; for it 
has been pointed out by Ehrlich that immunity may be produced 
against certain poisons derived directly from the vegetable kingdom, 
and that this immunity is dependent on the development of direct 
antidotes or substances capable of neutralising the poisons employed. 
Abrin and ricin, the poisonous principles respectively of the 
Jequirity and castor oil beans, are extremely active poisons; ricin 
being the more deadly of the two. Ehrlich estimates that one 
gramme (15i grains) of this substance would suffice to kill 1,500,000 
guinea-pigs. "And a drop of either poison in very dilute solution 
(1 in 50 — 1 in 100) introduced into the eye of a mouse causes 
acute inflammation and speedy destruction of the organ. Yet 
if mice be fed for some weeks with minute but gradually increasing 
quantities of abrin or ricin they become so far immune to the 
poison employed that they are able to resist an injection of from 
200 to 400 times the fatal dose for mice which have not under- 
gone this immunising process. Moreover, the strongest possible 
solution of abrin or ricin is without effect upon the eye of the 
immunised animals. But, as in the case of bacterial toxines, immunity 
to one poison gives no protection against the other. An animal 
proof against ricin is susceptible as ever to the action of abrin } and 
vice versa. m -nr 
A very remarkable circumstance is that the milk ot a mouse 
immunised to one of these poisons is found to confer a like immunity 
on young mice suckled with it. And the same phenomenon is observed 
in the young suckled by a mouse immuned to tetanus. 
