478 THE BLOOD [CH. XXIX. 



Anaphylaxis. The word anaphylaxis dates 'from 1905 and was 

 coined by Kichet ; he was studying the action of poisons obtained 

 from the sea anemone, and he found that if a small dose which 

 caused no symptoms in a dog was followed a week or two later by 

 the same small dose, the animal became ill and usually died. This 

 increased susceptibility lasted a considerable time, and he called it 

 anaphylaxis (ana against, phylaxis protection). Since this time it 

 has been found that most antigens produce a similar condition, but 

 the phenomenon was really known before Bichet gave it its name. 

 For instance, in vaccination the incubation period is four days ; in a 

 second vaccination this period is shortened, and the increased power 

 of the body to respond readily is in this case not harmful but 

 beneficial. Similarly, the tuberculous patient is hypersensitive to 

 tuberculin. Anaphylaxis has been largely studied in the guinea-pig, 

 and it is remarkable how small is the dose of a foreign protein which 

 produces the exaggerated sensitiveness. A millionth part of a cubic 

 centimetre of bone serum is often enough. Very small amounts also 

 will produce a serious condition or even a fatal result when the second 

 dose is given. In face of such small figures it seems hopeless to 

 isolate the toxic principle. The hypersensitive state may be trans- 

 mitted by the female guinea-pig to her offspring. Death, when it 

 occurs as the result of a second dose, is usually a matter of minutes 

 only ; the blood pressure falls enormously, the abdominal viscera are 

 gorged with blood, and haemorrhages are frequent; the bronchial 

 muscles are also acutely constricted. Numerous theories have 

 been advanced to explain these remarkable facts, and numerous 

 names, such as anaphylactin, sensibiline, etc., have been invented 

 for the supposed toxic material. There is some evidence that the 

 precipitin content of the serum runs parallel with the severity of 

 the symptoms, and that this is the factor to which the difference 

 between the normal and the sensitive animal is due. But how the 

 interaction of precipitin and antigen produces the symptoms is 

 entirely a matter of speculation. 



