92 
Nevertheless we devoted much time and study to the relation of 
this toxic principle to various chemical, physical, and electrical 
influences. The practical importance of eliminating or neutraliz- 
ing this toxic principle in horse serum is at once evident. 
It is probable that when the strange proteid is introduced into 
the guinea pig it causes a reaction resulting in a production of 
“antibodies/’ so that when a second injection of horse serum is 
given there is probably either a union or a reaction between the 
antibodies and a substance in the horse serum which produces the 
poisonous effect. 
This poisonous principle is quantitatively specific; that is, guinea 
pigs treated with horse serum are rendered somewhat susceptible 
to the subsequent injection of the serum of another animal. Guinea 
pigs treated with the serum of another animal are slightly sensitive 
to the toxic action of horse serum. 
Guinea pigs treated with the serums of various animals and sub- 
sequently injected, are much more susceptible to homologous serums 
than to heterologous serums. 
This poisonous action has no relation to hemolysis. Our work 
proves that blood serum may contain an acute poison entirely inde- 
pendent of any hemolytic action. Normal horse serum has no lytic 
power upon the red corpuscles of the normal guinea pig. 
This poisonous action has no relation to the specific albuminous 
precipitins. 
The poisonous principle in horse serum is not affected by a tem- 
perature of 60° C. for 6 hours, but it is destroyed at 100° C. for 15 
minutes. 
The poisonous principle is filterable through porcelain, is not 
injured by drying, and can not be separated by precipitation with 
ammonium sulphate and subsequent dialysis. 
The following chemical substances do not oxidize, neutralize, or 
precipitate the poisonous principle in horse serum: Butyric acid, 
permanganate of potash, citrate of soda, alcohol, succinic peroxide 
acid (alphozone) , hydrogen dioxide, and ammonium sulphate. The 
presence of chloroform or trikresol (0.4 per cent) does not interfere 
with this poisonous action. 
Serums eight years old are as toxic as those freshly separated. 
Exposure to X-rays does not affect the poisonous action of horse 
serum. 
It requires about 10 days after the first injection of horse serum 
for a guinea pig to show susceptibility to a second injection. A 
guinea pig remains susceptible a very long time, at least 160 days. 
As small a quantity as liUO /ooo c. c. of horse serum was sufficient 
in one instance to render a guinea pig susceptible. Quantities 
