622 SCIENCE PROGRESS. 



allowed to act. Ten minutes at 75°C. destroys the sub- 

 stance, and an hour at 57°C. causes a diminution of effect. 

 Merely heating to 6o°C. does not deprive serum of its 

 power (i, 14^). 



What has been said hitherto relates nearly entirely to 

 animals, and, of these, to guinea-pigs. We shall now 

 consider the question mainly in relation to man. 



The serum of normal guinea-pigs rarely exhibits 

 agglutinative power, but that of some other animals, 

 particularly of the horse, sometimes show it in a marked 

 but varying degree. So, too, does the serum of man. The 

 blood of many individuals possesses a pronounced agglo- 

 merating action on several forms of micro-organisms ; but 

 the quantity of each agglutinin is small, not showing itself 

 when the serum is diluted more than eight times (7^). 

 Thus normal human serum presents some striking differ- 

 ences from that of immunised guinea-pigs, principally in its 

 multiple action. We shall consider later whether this is 

 due to the presence of a common agglutinin or small 

 quantities of each special agglutinin. 



When normal serum has any agglomerating action it is 

 often nearly equal on at least three kinds of bacteria — B. 

 typhosus^ the cholera vibro and B. coli coiunmnis — and its 

 action on each disappears at about the same degree of 

 dilution. In one diseased condition marked by the evident 

 presence of abnormal substances in the serum, namely 

 jaundice, the agglutinating action is always present ; and if 

 the serum be not diluted, it is as rapid and complete as with 

 the serum of an immunised animal. Neither normal nor 

 icteric serum, however, possesses the power of inhibiting 

 movement. For this reason it seems probable that during 

 the process of immunising there are formed in the specific 

 sera two substances, one to cause the agglomeration and 

 another to inhibit movement, for this latter quality is nearly 

 as characteristic of such sera as the former. 



If this agglutinative property carry with it a proportion- 

 ate amount of immunity then a considerable number of 

 individuals are slightly immunised against typhoid, against 

 cholera, and probably also against other diseases. 



