IMMUNITY 267 



opsonin for one species of bacteria may be exhausted from a serum without 

 lessening in any way the opsonic content for other species of bacteria. 



When a patient suffers infection his opsonic content is primarily below 

 normal for the infecting organism; if the disease progresses to a favorable ter- 

 mination the opsonic content of the patient's serum, for the infecting organism, 

 shows a progressive increase from shortly before or after the disease reaches its 

 fastigium until recovery, and it may be distinctly above normal in the period of 

 convalescence continuing so for weeks or months. 



Vaccines produce a similar effect. Following the administration of a dose 

 of bacteria or bacterial extractives there is a sharp fall in the opsonic content, 

 the degree and duration of which is proportioned to the dose; this period of 

 depression is known as the "negative phase." 



An overdose (poisonous dose) of vaccine frequently induces a negative phase 

 of long duration followed by a slow return to normal. In a few favorable 

 instances an overdose is followed by a marked fall of short duration superseded 

 by a rapid elevation above normal. Therapeutic or immunizing doses produce 

 a slight negative phase of 12 to 72 hours duration followed by a gradual rise, 

 2 to 12 days in duration, averaging a distinct elevation of the opsonic content 

 above that which existed prior to treatment. 



Slight fluctuations in the opsonic content for the infecting organism during 

 the course of a disease frequently are not associated with discernible changes in 

 physical signs but marked fluctuations usually are, descent of the opsonic con- 

 tent being associated with physical signs of ill omen and ascent concomitant 

 with favorable changes in physical signs. 



OTHER PROTECTIVE SUBSTANCES IN BLOOD SERUM 



Previous descriptions of agglutinins, lysins and antitoxins explain in part the 

 stimuli causing production of such of these as are acquired, their degrees of 

 specificity and mode of action and their more important physical properties 

 and effects. 



There are specific agglutinins, lysins, precipitins and antitoxins present in 

 the blood serum prior to infection or inoculation. These form part of the 

 natural protective armament against infection. In general, primary anti- 

 bodies are less abundant and less effective than those formed as a result of 

 infection or inoculation (acquired antibodies) but are identical in nature and 

 action. 



There are notable exceptions to this rule as evidenced by immunity to 

 diphtheria. Schick and Park have shown that about 75 per cent, of all children 

 are immune to diphtheria during the first 3 months of life; during the remainder 

 of the first 2 years only 50 per cent, are immune; the percentage of children 

 immune to diphtheria gradually increases from the second year of life up to 

 maturity, at which time about 80 per cent, are immune even though they have 

 not had the disease. Evidence indicates that this immunity is largely, if not 

 entirely, due to the presence of antitoxin in the blood. Here then is an example 

 of natural antitoxin present in sufficient quantity to protect against infection; 



