RELATION OF LEUKOCYTES TO IMMUNITY 303 



in the blood serum only because changes in the leukocytes take place 

 during coagulation. It is not, by any means, settled that Metchni- 

 koff is right in this in fact, more recent investigations seem to show 

 that he is wrong, and that we may assume definitely that alexin is 

 present in considerable amounts in the circulating blood plasma of 

 normal animals. 



MetchnikofFs denial of this is based chiefly on the experiments 

 of Gengou. Gengou 17 took the blood from various animals into 

 paraffined tubes and centrifugalized it at low temperature before it 

 could clot. This freed the plasma from the cells before clotting, 

 though coagulation of course took place as soon as this plasma was 

 removed to tubes and kept at room temperature. The serum ex- 

 pressed from this clotted plasma he compared for alexin contents 

 (bactericidal properties) with that obtained from clotted whole 

 blood. 



He found that, in all cases examined (dogs, rabbits, and rats), 

 the plasma contained practically no bactericidal substances, or at any 

 rate an incomparably smaller amount than was present in the serum 

 obtained from the clotted blood. 



These experiments of Gengou would be conclusive in establishing 

 MetchnikofFs theory if they were confirmed by other observers. 

 This, however, has not been the case. Petterson 18 found no differ- 

 ence between the bactericidal properties of serum and oxalate plasma, 

 and Lambotte 19 arrived at similar results when he compared serum 

 with the coagulable plasma obtained by tying off a section of a vein 

 and centrifugalizing the blood without opening the vessel. Hew- 

 lett, 20 Falloise, 21 Schneider, 22 and more recently Dick 23 and Addis, 24 

 whose work has been done with particular attention to technical 

 accuracy, fail to confirm Gengou, finding no appreciable difference 

 between plasma and serum. 



In favor of Gengou' s results are the investigations of Herman 25 

 and the more recent ones of Gurd. 26 Further supporting Gengou's 

 conclusion is the observation recorded by a number of workers (Wal- 

 ker, 27 Longcope, 28 and others) that the complement or alexin con- 

 tents of serum will increase somewhat as the serum is allowed to 



17 Gengou. Ann. de I'Inst. Past., Vol. 15, 1901. 



18 Petterson. Arch. f. Hyg., Vol. 43, 1902. 



19 Lambotte. Centralbl. f. Bakt., Vol. 34, 1903. 



20 Hewlett. Zeitschr. f. Heilkunde, 24, 1903. 



21 Falloise. Bull, de VAcad. Eoy. de Med., 1905. 



22 Schneider. Arch. f. Hyg., 65, 1908. 



23 Dick. Jour. Inf. Dis., Vol. 12, 1913. 

 2 * Addis. Jour. Inf. Dis., Vol. 10, 1912. 



25 Herman. Bull, de VAcad. Eoy. de Med., 1904. 



26 Gurd. Jour. Inf. Dis., Vol. 11, 1912. 



27 Walker. Jour, of Hyg., 3, 1903. 



28 Longcope. Med. Bull. Univ. of Pa., 1902, Vol. 15, p. 331, 



