402 Dr. J. Mellanby. [June 3, 
Thus heating to 66° C. coagulated a little fibrinogen, but destroyed no 
antitoxin ; but heating to 77° C. removed the greater part of the coagulable 
protein and also the greater part of the antitoxin. 
The fact that diphtheria antitoxin can be heated up to 66° C. without 
destruction is interesting. Ferments and complements are stated to be 
destroyed when heated to 56°C. The greater stability of diphtheria antitoxin 
to heat differentiates it from these classes of bodies. 
The Electrolysis of Antitoaic Serum. 
When a constant current is passed into serum through zine sulphate 
electrodes, a mass of insoluble protein accumulates at the anode and water 
comes out at the cathode, the relation between the water and insoluble 
protein being such that the concentration of solids in the electrolysed serum 
keeps constant. The influence of this procedure on antitoxic serum was 
determined. 
A constant current at a pressure of 100 volts was passed into antitoxic 
serum through zine sulphate electrodes for three hours. A considerable mass 
of insoluble protein accumulated at the anode and an equivalent quantity of 
water passed out at the cathode. At the end of this time the antitoxic value 
of the remaining serum was determined. This value was found to have 
remained constant; the antitoxin had neither accumulated nor diminished in 
the remaining serum. 
This fact is capable of only one explanation—that diphtheria antitoxin 
possesses the same properties as the normal proteins of serum when tested 
by means of an electric current passed into it through zinc sulphate 
electrodes. 
The protein mass which accumulated at the anode was also tested for 
antitoxin. This precipitate consists of a zinc sulphate compound of protein. 
The precipitate was dissolved in a minimal quantity of sodium hydroxide, 
and its antitoxic value determined. It was found to have an antitoxic value 
proportional to the amount of protein dissolved. ‘This fact is interesting— 
the combination of the protein with zinc sulphate, although causing an 
insoluble compound to be formed, had not produced any chemical change. 
The resulting precipitate possessed the antitoxin value of the original protein 
when adequately dissolved. 
The Precipitation of Diphtherra Antitoxin. 
(A) By Alcohol.—The alcohol precipitation limits of horse serum containing 
400 units of antitoxin in each cubic centimetre were determined. The 
following results were obtained :— 
