VACCINES EOGER. 465 



like an antiseptic or an antidote. The organism itself, under the 

 influence of the vaccine, secretes certain substances, or, better, modi- 

 fies the condition of the blood, and this liquid is given new properties. 

 Immunity results not from a simple impregnation by useful products, 

 but from a reaction against harmful products. For this active im- 

 munity to be established, a certain amount of time must be allowed 

 after the time of vaccination. When it is necessary to act quickly — 

 for instance, when a foreigner arrives in a country swept by cholera 

 or the plague — instead of a bacterial vaccination, it is preferable to 

 use serum from an animal rendered immune. The two methods must 

 not be confounded. Serotherapy, or serovaccination, consists in 

 treating or rendering a person immime by means of a blood serum 

 of an animal previously vaccinated. The animal has received the 

 microbe-bearing product and has reacted from it; he has acquired 

 active immunity. The serum of his blood acts almost like an anti- 

 septic or a specific antidote. From the time that it impregnates a 

 new organism it protects it from infection and the organism does 

 not need to react; it takes no part in the action. Thus, it is said, 

 as opposed to the preceding case, that a serum produces a passive im- 

 munity. 



Passive immunity develops rapidly but is not lasting. The two 

 methods of procedure may be combined — the serum in alcohol may 

 be injected, followed by the vaccine, or, better, an injection of a 

 mixture of the serum and vaccine may be made. 



Starting from these results M. Besredka has proposed a new 

 method — vaccination by sensitized virus. The microbes placed in 

 contact with the serum from a vaccinated animal are impregnated 

 with this serum and lose their means of defense. They can no longer 

 resist the phagocytes — that is, the cells capable of absorbing and de- 

 stroying them. At present they are called sensitized. But an excess 

 of serum is more harmful than useful. So it is necessary to take 

 care, before injecting the microbes impregnated with the serum, 

 to wash them carefully in salt water. This is a new method which 

 has already been applied to a large number of diseases. Metchnikoff 

 and Besredka recommend it as efficacious against typhoid fever, and 

 after experiments made by them on chimpanzees they conclude that 

 it is superior to all other methods of procedure. 



The bacterial vaccines serve, as we have said, in rendering normal 

 organisms immune from danger of infection. It has been asked 

 why they would not be useful in fighting an existing infection. As 

 a result there has arisen a new method given the name of vaccino- 

 therapy, or, better, bacteriotherapy. 



The first trial is due to Koch, who proposed to combat tuberculosis 

 by injecting into subjects a special product, tuberculin, which is only 

 18618°— SM 1915 30 



