46 TJ niversity of California Publications in Zoology [Vol. 11 



tainly of interest as denoting the formation of a specific antibody, 

 or a deviation of complement, in the sernm of the infected fowl 

 by an infection of epithelioma eontagiosum. 



It is also of interest to note, in this connection, that antibodies 

 are most strongly developed in the presence of protoizoan infec- 

 tions and that this evidence, in so far as it goes, tends to support 

 the protozoan hypothesis as to the etiological factor in epithelioma 

 eontagiosum. 



Appearance of Specific Antibody. — While blood was taken 

 from four or five diseased fowls almost daily for a period of 

 almost four weeks, we are not prepared to say definitely at just 

 what stage of the disease the antibody is first present. However, 

 we were unable to find it present to any marked degree until the 

 lesions were fairly well marked, except in those where the method 

 of inoculation was intravenous injection, when it seemed to appear 

 earlier. In any haemolytic system, the addition of normal serum 

 may at times produce fixation, but that this was not so in our 

 series is shown by the contrast between the amount of fixation 

 in tubes, one of which contained serum from a normal healthy 

 fowl, and another of which contained an equal amount of serum 

 from an infected fowl taken under exactly the same conditions. 

 Each set was carefully controlled (see table 3) and on every 

 occasion when the controls indicated that none of the factors of 

 the haemolytic system was at fault, there was uniforml.y mark- 

 edly more fixation in the tubes containing serum from fowls hav- 

 ing epithelioma eontagiosum than in those having like amounts 

 of normal fowl serum. The following are the results of a single 

 day's experiment and are given because they are typical of the 

 results obtained on many days. The numbering of the tubes 

 corresponds to that in table 3. 



