PHYSIOLOGICAL 353 



in the complex colloidal mixture that we call the serum of the blood, 

 such that it looks as if anti-toxins counteracted toxins. Yet, all 

 theory apart, immunisation has already done much for the relief 

 of man's estate. 



8. Anaphylaxis. — Closely related to these phenomena of 

 immunity, though at first sight in disharmony with them, is "ana- 

 phylaxis". It an animal is first treated with a small dose of antigen, 

 so that anti-bodies are formed, and some ten days are then allowed 

 to elapse before introducing a further and perhaps very small 

 amount of the same antigen, "anaphylactic shock" immediately 

 supervenes. The symptoms of this vary in different animals, from 

 violent and rapidly fatal asphyxial convulsions in guinea-pigs to 

 much milder disorders — often only a severe rash — in man. These 

 dramatic results can be shown to follow the injection in two doses 

 of an amount of foreign (and possibly quite harmless) protein, 

 much less than that which the animal could easily survive in a 

 single dose. 



It seems likely that in anaphylaxis the reaction between antigen 

 and the anti-body formed by the first injection takes place, not in 

 the blood, but in the cells of the tissues. For example, if suitable 

 smooth- muscle tissues from a "sensitised" animal are treated, under 

 the proper conditions, with a small dose of the antigen, a violent 

 contraction will take place. Specificity is very marked in this case 

 also: it must be the same antigen that is introduced before and 

 after sensitisation. It is also clear that here again we are dealing 

 with a chemical reaction ; since a sensitised muscle preparation that 

 has once responded to a second dose of antigen by violent contrac- 

 tions will not again respond to a third dose : the anti-body that was 

 in the muscle cells has been used up. The reaction produced, it 

 should be noticed, is the same in any one species of animal, what- 

 ever the antigen selected is. 



As Dale, one of the leading workers in this field, has pointed out, 

 we have in anaphylaxis "the physiological response of an animal in 

 a certain phase of immunity to the artificial test which we impose", 

 and in no sense a negation of the practical defensive protection 

 that immunity confers on the body. 



9. Excretion. — As obvious end-products of the reactions of 

 metabolism we must reckon (i) carbon dioxide, which is volatile and 

 escapes from the body in the expired air, and (2) water, which 

 escapes from the lungs, from the skin, into the alimentary canal and 

 through the kidneys. There remain, however, (3) waste-products 

 containing the elements nitrogen, sulphur, and phosphorus, which 

 are not volatile, and are got rid of chiefly through the kidneys. 

 Although the duodenum, the colon, and the liver may have an 

 excretory function, their importance in this connection does not 

 seem to be very great. 



VOL. I AA 



