64 BACTERIOLOGY FOR NURSES 



normal, for as long a period as possible, thus constantly 

 preparing multiplying bacteria as palatable food for the 

 leucocytes, until the infected individual has become im- 

 miinized against the infecting organism. 



" The blood is examined on the first two or three days to 

 see whether or not there be a negative phase and to deter- 

 mine the maximal rise of the opsonic index. The negative 

 phase consists in the index falling lower than it was when 

 the vaccine was given, and has occurred but rarely in our 

 experience. On the sixth or ^seventh day the index is 

 again determined, and as soon as it falls to one or below, 

 another injection is given. Although there are many 

 chances for error in the technique, we sincerely feel that 

 the opsonic index is a valuable guide in regulating the 

 time and size of the dosage, and should be carefully fol- 

 lowed until we find a better guide." (Vail and Lincoln.) 



Ehrlich's ' "receptor theory" is an explanation of the origin 

 and action of antitoxins and bactericidal substances in 

 the blood of the immune. The subject is too profound 

 and complex to be embodied in a book of this character. 



In acquired immunity the blood-serum sometimes 

 acquires the property of agglutinating the bacteria, 

 causing the infection. This agglutination or clump- 

 ing is brought about by the presence in the blood- 

 serum of an anti-body that has the property of 

 bringing about the clumping of the bacteria and 



' Paul Ehrlich, Director of the Royal Prussian Institute for 

 Experimental Therapy. Studies in Immunity. 



