48 LECTUEES ON BIOLOGY 



hardened himself in this manner against poison, as a protective 

 measure against the poisoner, no poison was found strong enough 

 to kill him when on the collapse of his sanguinary career he 

 wanted to make an end of his miserable life. 



The power of the living organism to become accustomed to 

 poisons rests on the faculty peculiar to it of creating for each 

 toxin an antitoxin which will neutralize the ill-effects of the 

 toxin, unless the quantity introduced has been too large. But 

 prudent Nature always forms more antitoxins than are required 

 for the relevant purposes of neutralization. This surplus is 

 stored up in the tissues of the body where it lies ready for 

 any subsequent attack. Unfortunately, the curative effect of 

 these antitoxins is strictly specific, so that, for instance, an 

 acquired habit of taking arsenic is a protection only against 

 arsenical poisoning, but not against the ill-effects of morphia 

 or opium. 



We know to-day that the devastations of many species of 

 bacteria the causes of most of the infectious diseases are 

 due to the effects of certain specific toxins which, themselves 

 the results of the mode of life of these minute organisms, far 

 exceed in destructive power all other animal, plant, and mineral 

 poisons. Whilst 120 to 130 milligrammes of strychnine consti- 

 tute a fatal dose, only 0'23 milligramme, i.e., about the five- 

 hundredth part, of Bacillus tetani, the cause of lockjaw, is 

 sufficient to kill a man of about 70 kilogrammes body- weight. 

 But in spite of this truly awful power the animal body is capable, 

 to a certain extent, of becoming accustomed to bacterial poisons. 

 An instance of this experience is protective inoculation, as it has 

 been practised in Germany and in other countries against small- 

 pox and other infectious diseases for many years. Vaccination 

 does nothing else but cause in the body of the vaccinated 

 individual the production of a small-pox antidote which retains 

 for several years the power to annihilate, in the event of an 

 epidemic, automatically any small-pox disease germs that may 

 invade the organism. We cause, in fact, at first artificially 

 such slight cases of small-pox as the organism is able to with- 

 stand, in order to enable it in the future to escape severer 

 attacks. The great reduction in the number of cases of small- 

 pox in Germany since the passing of the Compulsory Vaccination 



