GERMICIDAL SERA 217 



thermore, an inactivated leukocytic extract from a guinea-pig can 

 be activated by the addition of a small amount of the normal serum 

 of a rabbit. 4. Extracts from the polynuclear leukocytes of rabbits, 

 guinea-pigs, and cats destroy in vitro the timothy, grass and butter 

 bacilli. The extracts from rabbits' leukocytes have a bactericidal action 

 on the bacillus tuberculosis of man. Extracts of rabbit, guinea-pig 

 and cat macrophages (mononuclear cells) do not destroy these acid- 

 fast bacilli in vitro. The same is true of the extracts from the thymus 

 glands of rabbits. Living polynuclear leukocytes injected into guinea- 

 pigs decrease the virulence of the bacillus tuberculosis of man. The 

 leukocytes of the guinea-pig do not have this effect. This must 

 suffice to show that the intracellular and extracellular germicidal con- 

 stituents of the blood are not the same and we will now return to a 

 consideration of the germicidal action of blood serum. 



Buchner named the germicidal constituents of serum, "alexins" 

 (defenders). These are inactivated at from 56 to 58 C. At first he 

 believed alexins to be protein bodies, but later he regarded them as 

 proteolytic ferments or enzymes. He did not succeed in isolating the 

 alexins, but he believed that they are secretions of the polynuclear 

 leukocytes and he proposed that these should be designated "alexo- 

 cytes," which, however, has not been adopted. Metschnikoff holds 

 that the alexins from the polynuclear cells (microphages) are bac- 

 tericidal, while those from the large mononuclear cells (macrophages) 

 destroy red corpuscles and other animal cells. He designates all 

 alexins as cytases and divides these according to the cells supposed 

 to secrete them into microcytases and macrocytases. However, it 

 has not been demonstrated that the production of alexins is limited 

 to the leukocytes, both mononuclear and polynuclear. Furthermore, 

 Metschnikoff did believe that alexins are intracellular ferments and 

 that their presence in blood serum is due to the dissolution of the 

 leukocytes and that there are no free alexins in blood plasma, except 

 possibly a trace due to the physiologic dissolution of the leukocytes. 

 As has been seen, this view is no longer tenable. 



It was shown by the work of Metschnikoff and Bordet that a 

 germicidal serum which has been inactivated by heating to from 56 

 to 58 C. may be reactivated on the addition of fresh serum. Further 

 work has shown that the bacteriolytic substances, present in both nor- 



