INTRODUCTORY 5 



salt solution to make up to the same bulk in each tube, say 

 1-5 c.c. A rough test can thus be made, and then a more 

 accurate estimation carried out in a similar way. The 

 dosage of immune-body having been thus obtained, the 

 minimum haemolytic dose of any complement (fresh normal 

 serum) can be estimated by a similar procedure, in this case 

 an excess of immune-body being added. It is to be noted 

 that if the minimum dose of immune-body and of comple- 

 ment be thus obtained by the above method, in most cases 

 the two minimum doses together will not produce complete 

 lysis. In other words, the minimum dose of immune-body 

 will only produce lysis with the optimum amount of com- 

 plement, which may be several minimum doses, as above 

 defined. A similar statement applies to the minimum dose 

 of complement. The optimum amount of complement 

 and of immune-body, respectively, as compared with the 

 minimum dose, varies considerably in different sera, and 

 it must be determined in each particular case. The ex- 

 planation of this phenomenon, which is still obscure, has 

 been discussed in a paper by Morgenroth and Sachs. 1 

 After the addition of immune-body and complement to the 

 red corpuscles, the test-tubes are placed in an incubator at 

 37 C. for two hours, and are then placed in a cool chamber 

 till next morning, when a reading is taken. Complete lysis 

 is shown by the contents of a tube being quite clear and 

 without any deposit. When subsequent tests or procedures 

 have to be carried out on the same day, the reading may 

 be taken when the tubes are removed from the incubator. 

 As has already been indicated, the lysis of the red cor- 

 puscles indicates the union of immune-body and comple- 

 ment with the receptors of the red corpuscles, but the 

 hsemolytic doses, as above explained, do not indicate how 

 much of these substances may enter into union. On the 

 contrary, as will be shown below, red corpuscles may take 

 1 Morgenroth and Sachs, Berlin. Klin. Woch., 1902, no. 35. 



