BLOOD AND THE IDENTIFICATION, ETC. 621 



by the injection, either hypodermically or into the peritoneal 

 cavity, of dead or attenuated cultures of the micro-organisms. 

 The destruction of the culture used may be effected by the 

 use of either heat or disinfectants, but too great an applica- 

 tion of either diminishes or destroys the immunising power 

 of the injection (14/^). The date on which the reaction first 

 appears after injection is rather variable, and depends on 

 two or three factors, although chiefly on the strength of 

 culture. Thus a guinea-pig which I injected with living 

 cholera culture on i8th April, 1896, showed the reaction 

 well on the 21st, whilst one injected with dead cholera 

 culture on i6th March. 1896, did not exhibit marked ag- 

 glutinative action till 23rd March. It is not even necessary 

 to inject the bodies of the bacteria : filtered cultures give 

 similar but weaker or more dela)ed results (14^, 9). By 

 the simultaneous injection of two kinds of micro-organisms 

 agglutinins for both can be produced in the same serum 



" Passive " immunisation is generally produced by the 

 injection of serum from an actively immunised animal. In 

 such a case the agglutinative property shows itself much 

 sooner. Thus, in a guinea-pig which I injected at 3 p.m. 

 on 9th March, 1896, agglutinin could be detected in the 

 blood already at 3*30 p.m., and had attained its maximum 

 strength about 6 "50 p.m., remaining at the same strength 

 for about one week afterwards. An actively immunised 

 guinea-pig generally possesses agglutinative serum for a 

 considerably longer period. 



The nature of the agglutinating substance has not yet 

 been distinctly ascertained. Filtration of the serum through 

 a porcelain filter diminishes its power. Precipitation by 

 neutral salts of the globulin of the serum or the fibrinogen 

 of the plasma causes loss, or sometimes only diminution, of 

 agglutinative power in the filtered fluid. Similarly serum 

 is generally only two-thirds as powerful as plasma, so that 

 the agglutinin seems to be in some way bound up with the 

 proteids of the blood. Leucocytes, when shed, do not 

 apparently give off any agglutinin. Temperature affects 

 agglutinin in proportion to its height and the time it is 



