president's address — SECTION L. 281 



Partly because many of the earlier isolated observations were 

 made on the guinea pig, and also because of its great susceptfbility 

 to anaphylaxis, this animal has been chosen for most of the 

 experimental investigations. The rabbit, dog, sheep, mouse, and 

 other animals have all been used, but, whilst they all show 

 anaphylaxis under proper conditions, they are less susceptible 

 than the guinea pig,, and the effects in them are less regular. A 

 ]3cint of primary importance is that, whatever the material used 

 for injection, whether bacteria, serum, or ceils, the symptons pro- 

 duced, and the poHt-mortem appearances and lesions in a fatal 

 case are the same. Eestlessness and anxiety, a subnormal tempera- 

 ture, a fall in blood pressure, and dyspnoea are prominent features, 

 whilst on post-mortem, examination the lungs show a condition of 

 acute emphysema, with the alveoli distended, the capillaries empty, 

 and the small bronchioles contracted so as to imprison the air in 

 the lungs. 



Again, it may be stated that the substances giving rise to 

 anaphylaxis are all of the nature of antigens, all able to provoke 

 the production of antibodies when injected into an animal. 

 Further, it is very remarkable how minute a dcse of the first 

 injection may be sufficient to sensitize. 



The firs-t injection may be made in .various ways, subcutaneous, 

 intraperitoneal, intravenous, but the most acute results are 

 obtained when the seco/id injection is made directly into the blood 

 stream. Material injected subcutanecusly is absorbed so slowly 

 as to be accommodated usually, ®r if symptoms of shock occur 

 they are delayed and subacute. Injected per rectum absorption 

 again is so slow that no dangerous shock results. For this reason 

 this method has been recommended to prevent any ill effects from 

 repeated injections of substances likely to cause anaphylaxis 

 (Besredka) . 



A time interval of at least ten to twelve days is necessary after 

 the first injection before the sensitive state is reached. This is 

 called the pre- anaphylactic period, but thereafter the animal re- 

 mains susceptible to a second injection of the antigen for a long 

 period, often many months. 



We have so far described active anaphylaxis, but, just as there 

 is a passive immunity, so there is a state of passive anaphylaxis. 

 This can be produced in a fresh animal by injecting into it the 

 serum of an actively ftensitized animal ; also with the serum of an 

 animal strongly immunized against any antigen, and, therefore, 

 itself containing antibodies. In fact, the power of a serum to 

 confer passive anaphylaxis is in. proportion to its content of anti- 

 bodies. This sensitive state does not as a rule occur immediately 

 after the injection of the immune serum, but develops in anything 

 from four to twenty-four hours after injection. 



