48 BACTERIA AND SOIL FERTILITY 



is so highly fatal. What a minute quantity of the pure compound 

 would be required to kill a man ! Experiments show that only a 

 few molecules of the botulinus poison, a poison sometimes found 

 in food, is required to kill small animals. 



3. Bacterial toxin if used in extremely small but increasing 

 doses will produce immunity. When a very minute trace of the 

 toxin gets into the body of an animal the cells commence to 

 manufacture an emergency material which robs the toxin of its 

 power. It is known as antitoxin, and the presence of this anti- 

 toxin in the blood of the individual means that he will not take 

 lockjaw, diphtheria, or whatever the specific disease. We then say 

 he is immune. The immunity may become so great that it makes 

 no difference how many of these poisonous darts are shot at the 

 individual by the microbe, they fall without piercing his armor 

 of immunity. However, it is different with strychnin. To this 

 the individual never becomes resistant. Man may become so he can 

 tolerate more nicotine, but give even the habitual tobacco user a 

 large dose of nicotine and it will kill him. 



4. Toxins have an incubation period, whereas most ordinary 

 poisons have not. If an animal receives strychnin it soon becomes 

 ill and quickly recovers or else dies. Whereas, if an animal is given 

 a bacterial toxin there may be a delay of days or even weeks be- 

 fore the symptoms appear. The time between the entrance of a 

 toxin into the body and the appearance of symptoms is known as 

 the incubation period. It varies with different toxins and also 

 with the quantity of toxin administered. 



5. Toxins are easily destroyed by drying, sunlight, heat, and 

 certain chemicals. Hence, any material containing bacterial 

 toxin, if heated throuout to 100° C. for fifteen minutes, will be 

 free from it. However, if strychnin had been in the substance 

 this would not be the case. A toxin may be heated and thus lose 

 its power of poisoning an animal but still retain its power of call- 

 ing out "antitoxin," thus rendering the animal immune to the dis- 

 ease. This is made use of very extensively in medicine to protect 

 us against disease. 



Ptomaines. — These are products formed when bacteria break 



