282 LECTURES ON IMMUNITY 



Bordet 1 early drew attention to the great difference 

 between rennet and lacto-serum, though both coagulate 

 milk (casein). The coagulation with rennet is much more 

 voluminous and gelatinous than that with lacto-serum, 

 which also gives precipitation at lower temperatures 

 (under 20 C.), very different from rennet. Furthermore, 

 lacto-serum is inactivated only by being heated for thirty 

 minutes to over 70 C., whereas a 2 per cent solution of 

 rennet loses its coagulative power in less than five minutes 

 at 50 C. (cf. p. 87). The lacto-serum is, on the other 

 hand, much more easily precipitated by ammonium sul- 

 phate than is rennet. A very important point is that the 

 coagulum of the lacto-serum yields no serum-albumen. A 

 similarity is that in both cases the presence of calcium or 

 barium salts is necessary for the precipitation, so that the 

 reaction is hindered by the presence of oxalates in the 

 milk. M tiller investigated other salts, viz. NaCl, KC1, 

 NH 4 C1, Na 2 HP0 4 , NaCH 3 CO 2 , NaNO 3 , KNO 3 , KI, 

 KBr, KSCN, and MgSO 4 , but none of them could replace 

 Ca salts. In this point there is a great distinction from 

 the agglutinations, which are rendered possible by the 

 most widely different salts (cf. p. 159) according to Fried- 

 berger. 2 The precipitins examined by Eisenberg do not 

 seem to need salts for their action. Many salts diminish 

 the action in even rather weak concentrations, thus, for 

 instance, (NH 4 ) 2 SO 4 in 0.25 normal solution and MgCl 2 

 in 2 normal solution completely check the precipitating 

 action. By heating the milk during some time to 100 C. 



1 Bordet: Ann. de VInst. Pasteur, 13. 241 (1899). 



2 Frierlberger : Centralbl. f. Bakteriologie, 30. 341(1901). Cf. Bechhold; 

 p. 159 above. 



