An antibody introduced into the circulation appears 

 to decrease in a very regular manner. At first, 

 when the amount of antibody is considerable, the 

 fall occurs very rapidly, but gradually it becomes slower 

 and slower. This is clearly seen from the preceding 

 paper 1 ) concerning the agglutinins in the circulatory 

 system of different animals. 



If we proceed to study the laws of such a phenome- 

 non as a regularly progressing fall, it seemed from the 

 first most perspicuous to figure the amounts as ordi- 

 nates (x) and the times as abscissse (t). When we try 

 to find the analytical equation of the curve thus defined, 

 it is natural to expect that there will be a simple rela- 

 tion between the velocity of change in the ordinates and 

 the coordinates of the corresponding point. 



After different attempts it was found that this rela- 

 tion could be expressed by a differential equation of 



the following form: 



dx 1 

 dt 



n and K being constants, which arc characteristic for 

 each case. 



Jargensen and Madsen: The fate of typhoid and cholera agglutinins during ac- 

 tive and passive immunisation. 



