ACQUIRED IMMUNITY 903 



EXPERIMENT 24. RELATIVE FACTORS IN NATURAL IMMUNITY 



1. Place a frog in a shallow vessel of warm water in the incubator at 37 C. 



2. After twenty-four hours give a subcutaneous injection of tetanus toxin equal 

 to one-tenth the fatal dose for a 300-gram guinea-pig. 



3. Inject a second frog with an equal amount of toxin and keep it at ordinary 

 room temperature in cold water. 



4. Observe both animals. 



(a) Do symptoms of tetanus develop in any of the animals? 



(b) Why does heat favor tetanus infection? 



(c) Give further examples of relative natural immunity. 



(d) Are anthrax bacilli found in the smears and cultures of both ani- 

 mals? Which animal is immune? Could phagocytosis play a role in 

 this immunity? 



EXPERIMENT 25. INFLUENCE OF TEMPERATURE UPON NATURAL IM- 

 MUNITY 



1. Procure dried tetanus toxin and dissolve sufficient in 6 c.c. normal salt solu- 

 tion equivalent to 6 lethal doses for a 350-gram guinea-pig. 



2. Inject 2 c.c. into the pectoral muscles of a young hen. Take the rectal tem- 

 perature. 



3. Inject 2 c.c. into a second hen. Take the rectal temperature and place her 

 in cold water until the temperature has dropped several degrees. 



4. Place hen No. 1 in a cage and keep her at ordinary laboratory temperature. 



5. Place hen No. 2 in a cage and keep her in a cold place or renew the bath 

 several times in order to keep her temperature subnormal. 



(a) What is the normal temperature of the hen? 



(b) Do both animals present symptoms of tetanus? 



(c) How do you explain the difference? 



6. If hen No. 1 does not show symptoms of tetanus by the second day, reinject 

 her with an amount of toxin equal to 10 lethal doses for a guinea-pig. 



(a) Does this hen present evidences of tetanus? 



(b) If so, how do you explain the result? 



EXERCISE 9. ACQUIRED IMMUNITY 



EXPERIMENT 26. ACQUIRED ACTIVE (ANTIBACTERIAL) IMMUNITY 



1. Immunize a rabbit with typhoid bacilli as described in the chapter on Active 

 Immunization. 



2. Inject this immune rabbit intravenously with 6 loopfuls of a twenty-four- 

 hour culture of Bacillus typhosus thoroughly emulsified in 2 c.c. sterile salt solution. 



3. Inject a normal rabbit of equal weight with an equal dose and in the same 

 manner. 



4. Both animals are weighed and their temperatures recorded before the injec- 



