172 INFECTION AND RESISTANCE 



as we can tell at present, therefore, we cannot accept, as conclusively 

 proven, the contention that the circulating plasma contains no alexin. 

 Nevertheless the Metchnikoff school have not been discouraged by the 

 various contradictions of Gengou's work, found in the experiments we 

 have enumerated, because they are not satisfied that the technique of 

 other workers has conclusively excluded cell injury. Owing to the 

 great difficulties of investigations of this kind, when carried out with 

 mammalian blood, it is not impossible that they are justified in this, 

 but nevertheless the assumption of the absence of alexin in the 

 plasma finds so many objections in other observations that the bur- 

 den of proof would certainly rest with Gengou and his supporters. 

 Not the least important of these objections, it seems to us, is based 

 on the very simple experiment of injecting bacteria into the veins of 

 a living animal and finding a very rapid and active phagocytosis. 

 And considering the very probable participation of alexin in the 

 opsonic functions this would seem to point strongly toward the pres- 

 ence of these substances in the circulating blood. The evidence also 

 furnished by the recent developments of our understanding of ana- 

 phylaxis would further tend to strengthen our belief in the presence 

 of alexin or complement in the normal circulation. For, in the 

 process, as we shall see in a later chapter, complement plays 

 an important role. When 3 per cent, salt solution is administered (as 

 in Friedberger's experiments), and the action of complement is 

 thereby inhibited, anaphylactic shock may be greatly diminished. 



It has also been claimed, chiefly by Walker 20 and by Henderson 

 Smith, 21 that, as serum stands upon the clot it at first gains in alexin 

 or complement contents, an occurrence which they attribute to the 

 liberation of alexin from the leukocytes. This observation has not 

 been universally borne out and, even were it unquestionable, it might 

 be dependent upon any one of the numerous factors involved in the 

 complicated process of coagulation rather than upon leukocytic 

 changes only. 



The failure to obtain definite proof of the origin of alexin from 

 the white blood cells has led to search for the source of these sub- 

 stances in various organs. An interesting series of investigations 

 on this subject are those of Mile. Louise Fassin, 22 who believes that 

 she has found reasons for definitely associating the thyroid gland 

 with alexin production. She found that the subcutaneous injection 

 of thyroid extract into dogs and rabbits was followed by a rapid 

 increase of alexin, both hemolytic and bactericidal, and that the 

 same thing was true when thyroid substance was administered by 

 mouth. When the thyroid gland was removed from rabbits a reduc- 

 tion of alexin resulted. Although important, these researches do not 



20 Walker. Journ. of Hyg., Vol. 3, 1903. 



21 Smith. Proc. Roy. Soc., Series. B, Vol. 79, 1906. 



22 Louise Fassin. C. R. de Soc. BioL, Vol. 62, 1907. 



