Immunization against Cyanolophia. 157 



by chance, with four other chickens but without success. We 

 could only note a retarding of the incubation period. But with 

 serum No. 13 we could gain passive immunity of an untreated 

 chicken, No. 21. 



At this stage of my work I left Germany and continued my 

 experiments in this country at the Osborn Zoological Laboratory 

 of Yale University, from October, 1915, up to the present time. 



My problem was to find out which of these various factors 

 von Wassermann and I had used in Germany were necessary to 

 produce active immunity, which were not necessary and could be 

 omitted, and which new factors had to be added to produce 

 immunity — not by chance but by a graded series of experiments- 

 It was not necessary to try to gain immunization with serum 

 treatment alone because these experiments had been made by 

 various authors. (See Maggiora and Valenti(i).) Also it was 

 not necessary to try to gain immunization by a treatment with 

 virulent brain alone which had been attenuated by staying long 

 periods in glycerine. (See von Prowazek (2).) Nor did it seem 

 advisable to try to gain immunization by applying to the chickens 

 doses of desiccated brain alone. (See Kraus (3, 4, 5).) My own 

 experience, which I reported here in May, 1916, in trying to im- 

 munize with attenuated serum and bone marrow tissue culture 

 alone had not been successful. I could only show that the in- 

 cubation period could be prolonged. It was certain that our 

 known methods of immunization ought to be varied or combined 

 because none of them alone produced results. Only the knowledge 

 that there is an active immunity induced me to go on in a rather 

 empirical way guided by the idea that it must be possible to raise 

 the resistance of the chicken against Cyanolophia by slight, nearly 

 unnoticeable attacks of the disease. 



From October, 1915, to July, 1916, I inoculated chickens with 

 desiccated brains on a large scale. These brains 1 had been taken 

 from chickens which died of Cyanolophia after a very prolonged 

 incubation period. Of these brains I had six which are called 

 in the following Table No. 1, Des. 1 to Des. 6. Table 1 gives an 

 exact survey of the chickens and shows how often each one had 

 been inoculated with the different desiccated brains. 



1 N. B. For details concerning the method of preparing the different protective 

 materials, the exact amount of them, etc., see the main paper. 



