14 COLLECTED STUDIES IN IMMUNITY. 



serum, the immune body as well as the addiment, in a free state. 

 In the ordinary specific hsemolytic serum the former is usually readily 

 obtained because the addiment is destroyed by slight heating. In 

 the case of our serum, however, heating proved ineffective, so it 

 became necessary to adopt other means. Experience having taught 

 us that the addiment is, as a rule, more readily destroyed than the 

 immune body, we could expect to accomplish our purpose by using 

 stronger destructive agents of a chemical nature. After a number 

 of trials we have finally made use of the following procedure: 

 One part of our serum is mixed with one-tenth part normal hydro- 

 chloric acid, the mixture digested at 37 C. for 30 to 45 minutes, 

 and then neutralized. It will be found that the serum has then lost 

 its solvent power for sheep blood-cells; but that it still possesses 

 immune body in scarcely decreased amount can be shown by re- 

 activating the serum. 



The isolation of the immune body made it possible finally to demon- 

 strate the combination of the immune body at higher temperatures, 20- 

 35 C. This combination is seen to be quantitative, i.e., the sheep blood- 

 cells are able to combine with all the immune body present in that quan- 

 tity of serum which in its active state would just suffice for their com- 

 plete solution. For example, to 5 cc. of the 5^ blood mixture, 0.15 cc. 

 of the serum inactivated with hydrochloric acid is added, it having 

 been previously ascertained that this amount of active serum just 

 suffices for complete solution. The mixture is allowed to stand 

 for half an hour at room temperature and is then centrifuged. To 

 the sediment 2.0 cc. normal goat serum are added, and to the clear 

 fluid some additional sheep blood mixture and 2.0 cc. normal goat 

 serum. The sediment thus treated will be seen to dissolve com- 

 pletely, whereas the blood-cells added to the clear fluid remain intact 

 despite the presence of the addiment. This shows that all the im- 

 mune body combined with the sedimented sheep blood-cells. 



The addiment necessary for this reactivation is present in normal 

 goat serum, as can be seen from the experiment. This is true for all 

 goat sera thus far examined by us, although the amount varies. 

 It will be recalled that we had found the original addiment which fitted 

 the immune body was able to withstand heat. The question there- 

 fore at once arises whether normal serum also contains such heat- 

 resisting addiments. As a matter of -fact this was found to be the 

 case in a number of goats examined by us. When the serum of these 

 goats was heated for ^ to f hr. to 56 C. and its normal hopmolytic 



