4 Nebraska Agricultural Exp. Station, Research Bui . 21 
the series (1) pertaining to the sera intended to be used in swine 
or (2) made with the aid of strains derived from swine, our 
swine strain No. 59 was employed. The virus used always con- 
sisted of bouillon cultures at the end of a twenty-four hour 
incubation. 
Rabbits were used as test animals. The serum was injected 
subcutaneously, while the virus was injected intravenously. The 
intravenous virus injections were preferred after previous ex- 
periments had shown that in this manner the annoying forma- 
tion of abscesses and necrotic areas could be avoided, while the 
difference between the results obtained with intravenous virus 
injections and subcutaneous ones was only expressed by a 
slightly shorter incubation period in the case of the former. 
For so far as this was possible each serum was utilized in 
two test series. In one of them there was variation in the doses 
of serum given. All the animals in this series received the 
serum on a given day, while the virus was injected twenty-four 
hours later. In the other series all the rabbits received ten c.c. 
of serum on a given day. The series was then divided into four 
or five groups, each of which received the required amount of 
virus at periods from three to five days apart. 
In the first series the influence of the amounts of serum was 
taken into consideration, while in the latter we aimed to obtain 
information regarding the duration of the passive immunity, in 
case any should be manifest at all. 
Second injections of virus were given to all surviving ani- 
mals, usually some two weeks -after the first virus injection was 
administered, with a view of ascertaining whether or not the 
subsequent injection of virus into a serum protected animal 
would engender a more enduring and active immunity. 
BOVINE STRAIN SERA 
The first series comprises the tests made with varying doses 
of serum. In one of the tests (No. 1052) a parallel number of 
rabbits were injected with normal horse serum in order to prop- 
erly appraise whatever nonspecific protective influence may be 
attached to a foreign serum per se. 
The details of the tests are exhibited in Tables 1-11. 
