SERUM THERAPEUTICS IN RESPECT TO TUBERCULOSIS. 799 
protective inoculations is to produce this state of insusceptibility 
or “immunity by introducing the specific microbes in a modified 
form, and so producing a modified form of the disease. As to the 
essential nature of the immune state, however, there has been much 
difference of opinion. 
There was first the theory of exhaustion , to which at one time 
Pasteur lent the aegis of his support. This theory assumes that the 
microbes of an infectious disease use up or exhaust the supply of some 
particular substance necessary for their development, and that this 
substance is not subsequently reproduced — and hence the immunity. 
This view is, I believe, now generally discarded. 
Then there was the retention theory of Chauveau. By this it 
was supposed that certain substances, produced by the activity of the 
microbes, accumulated in the system, and were subsequently retained, 
and, being prejudicial to the particular micro-organism that produced 
them, prevented future invasion. 
Another view regards immunity as dependent on an acquired 
tolerance of the poisonous products of any given pathogenic microbe. 
\et another, commonly known as the Phagocytosis theory of 
Metschnikoff, makes the white blood-cells {'phagocytes) , which 
undoubtedly do incorporate and probably destroy micro-organisms, 
the all-important agents in protecting the body against pathogenic 
bacteria. 
At the present time a quite different explanation of the pheno- 
menon of immunity is very generally accepted. Indeed, it rests upon 
such experimental and practical evidence as to leave little room for 
doubt as to its substantial correctness. This may be called the 
antitoxine theory. And since it is the basis of what I have to 
suggest as a possible means of treating tuberculosis, I may perhaps 
be permitted to enter into it a little more fully. 
This theory teaches that in response to the presence of the poison 
(toxine) generated by a given microbe there is produced in the system 
a specific antidote (antitoxine) which neutralises and destroys that 
poison. How and why this toxin-neutralising substance is formed, 
remains for the present a mystery. 
It must be remembered that this doctrine of antitoxine. s which, 
stated simply as an hypothesis, does not perhaps commend itself as 
having a pnma facie appearance of probability, has been established 
purely as the result of experimental investigations. 
It is well known that animals differ greatly in their natural 
susceptibility to different bacterial diseases. In the case of anthrax, 
frogs, dogs, and white rats, amongst other animals, enjoy complete 
immunity. Mice, however, are very susceptible. It has been found 
by Ogata and Joshuara that the blood serum of these naturally 
immune animals has a very wonderful effect in protecting susceptible 
animals from the disease. A single drop of frog’s blood, or half a 
drop of dog’s blood injected into a mouse, suffices to save it from the 
effects of anthrax inoculation that would be otherwise fatal. 
Results of a similar kind have been obtained by injecting the 
serum of animals artificially rendered immune (by inoculation, or bv 
the injection of the toxic products of virulent cultures). Behring 
and Kitasato, in their well-known experiments upon tetanus and 
diphtheria, have shown that if the blood serum of an animal rendered 
