70 THE RELATION OF BACTERIA TO DISEASE 



of dead cultures of the bacteria, responsible for the 

 condition, are made beneath the skin. The principles 

 of this treatment were discussed on page 66. The 

 progress of treatment is followed by a long elaborate 

 technique of permitting the leukocytes of the blood 

 of the patient, and as a control, those of a healthy 

 person, to feed upon the bacteria in question, in test- 

 tubes kept at body heat. If the number of germs 

 consumed by the patient's leukocytes rises during the 

 course of the treatment, he is considered as benefiting 

 from the injections. His general constitutional con- 

 dition is closely watched also. It is now attempted 

 to use for "vaccination" a culture made from the 

 patient's disease. 



The reader must not picture that these so-called 

 antibodies are substances that can be handled. They 

 are invisible chemical parts of the serum of the blood, 

 and only perceptible through extremely delicate labor- 

 atory procedures. The present conception of their 

 action was worked out by Dr. Ehrlich, a German 

 physician, chemist, and physicist. His theory, broadly 

 speaking, assumes a group of substances circulating 

 in the blood which can be stimulated to meet and 

 destroy invaders, and thereby protect the body. 

 Besides the three methods above outlined, in which 

 practical therapeutic use has been made of the known 

 facts in the study of immunity, still others have been 

 devised but they are scarcely yet out of their experi- 

 mental stage. 



