E. A. Watson 
169 
to cling firmly to the sides, the serum being separated with more or less 
difficulty. In small round bottles, curved into a narrow neck and mouth, 
for corks, filled with freely flowing blood to within a margin of the narrow¬ 
est diameter but not touching the cork, and allowed to stand for at 
least half-an-hour for coagulation, there is usually an abundance of 
clear serum. 
Such bottles, of one ounce capacity, one inch in diameter, three- 
eighths inch neck and mouth, are very suitable for field work. They 
must be absolutely clean and free from any trace of soap, alkali or 
acid. These bottles are distributed from this laboratory after being 
sterilized in the hot air oven, corked, labelled and well wrapped in sterile 
paper wrappers. Also, large bore needles attached to three inches of 
rubber tubing with a small glass nozzle, separately wrapped and sterilized. 
With this simple apparatus and observing the usual precautions during 
operation it is an easy matter to draw blood from the jugular vein of 
a horse, aseptically. 
Among the last 6000 samples of blood secured in this manner less 
than twenty have reached the laboratory in a condition unfit for 
testing and these few unfit specimens have been ten days or more in 
transit. 
On reaching the laboratory the specimens are briefly examined and 
where necessary the clots are detached from the sides of the bottles with 
a sterile wire. They are then left to stand in a cool chamber overnight 
for the serum to clear. The serum is then drawn off into small test 
tubes, about 2-0 c.c. in each, and is ready for inactivation. 
Inactivation of Serum. Before any specimen of horse serum can be 
used in the complement fixation test it has first to be inactivated. All 
animal serum in a very fresh state contains complement in a varying 
amount. This constituent is readily destroyed by heating the serum 
to 55-56° C. for one half hour. No complement other than that 
employed in the haemolytic system may take part in the reaction. 
As a matter of fact horse complement very rapidly becomes inert and 
in specimens several days old is a practically negligible quantity. How¬ 
ever, in normal horse serum there arise several other factors which, 
unless destroyed or rendered inactive, are able to act upon complement 
and antigen and disturb an haemolytic system. All untreated horse, 
donkey and mule sera possess enzymotic and proteolytic properties, 
potentially at least, and becoming active in sera a day or two old. 
They act upon most preparations of antigen, especially upon macerated 
