THE PARTIAL-FUNCTIONS OF CELLS. 683 



far been very meagre. The one example which may be familiar to 

 the reader is the fact demonstrated by H. Kossel that on long- 

 continued immunization of rabbits with the hsemotoxic eel serum, 

 the blood cells finally became insusceptible to this serum, as though 

 they had lost their specific receptors. 



Recently, aided by my colleagues, Dr. Rohl and Miss Gulbransen, 

 I succeeded in gaining an insight into the nature of the disappearance 

 of receptors. While the work will be made the subject of a special 

 paper, I may here say that our experiments were made on trypano- 

 somes. Working in my laboratory, Franke, after infecting a monkey 

 with a particular species of trypanosome, had cured the disease by 

 means of chemo-therapeutic agents, and had tested the immunity 

 of the animal by again infecting it with the original strain. Con- 

 trary to expectations, it was found that the monkey was not immune, 

 so that after a very prolonged incubation, the disease reappeared. 

 If mice were inoculated with blood from the diseased animal, i. e., 

 with blood containing trypanosornes, they became infected and 

 died. Curiously, however, if the trypanosomes were first removed 

 from this monkey blood, it was found that the serum was able to 

 kill the original strain of trypanosomes. This showed that the try- 

 panosomes had undergone some change in the body of the monkey, 

 and that the variety thus produced differed from the original strain 

 in its behavior toward the serum; it had become serum-fast. 

 Similar observations were made at the same time by Kleine, and 

 recently also by Mesnil. 



We found that when animals which had been infected with a 

 particular strain of trypanosome were treated with less than the 

 complete sterilizing dose of suitable substance (arsanil, arsazetin, 

 arsenophenylglycin) the trypanosornes disappear from the blood for 

 a time. It can easily be shown that in this case also antibody has 

 been produced. The few parasites which escape destruction lie 

 dormant in the body for a time and gradually adapt themselves to 

 the antibodies present in the serum. Then they again pass into the 

 blood, where they rapidly multiply and bring about the death of the 

 animal. We inoculated the trypanosomes so obtained into two 

 series of mice. One series consisted of mice which had been infected 

 with the original strain and then cured with suitable doses. These 

 animals, therefore, possessed specific antibodies. The other series 

 consisted of normal mice. Infection resulted equally rapidly hi 

 both series. This shows that the parasites of the strain producing 



