1908.| -  Duphtheria Antitoxin. 401 
The crystals obtained when dissolved in water did not possess antitoxic 
properties. 
It is evident, therefore, that diphtheria antitoxin belongs to or is associated 
with that great group of albumins which compose about 85 per cent. of the 
total protein of serum. For this class of albumin no method of physical 
differentiation has been obtained. It was interesting, therefore, to determine 
whether a delicate biochemical test such as is involved in the standardisation 
of diphtheria antitoxin would permit of a further differentiation. 
The Freezing of Serum. 
Serum containing 400 units per cubic centimetre of diphtheria antitoxin 
was frozen in a long cylinder and allowed to melt gradually. The resulting 
liquid was syphoned off in a series of layers. Antitoxin tests were made on 
some of the fractions and the relation of the antitoxic value to the percentage 
of protein determined. The following results were obtained :— 
Amount of solid 
in 100 ce. Antitoxic value. 
PPOA OUAMIMME SR: oe 6. eo de «e 50+ 
pm ee emma LS) 200+ 
9-06 poe tent LS. 300+ 
13°19 Pu PRAM NSS hon 450+ 
17:08 Dae cent eas tlt 700+ 
Original serum... 9°4 AS Laie oar Hea ae 400 
The + sign above indicates that the animals survived the tests without any 
serious symptoms. The results are conclusive,—the concentration of antitoxin 
follows the concentration of the protein on approximately parallel lines. 
The Heating of Serwm. 
The relation of diphtheria antitoxin to the proteins of serum coagulable by 
heat was determined. 
Serum containing 400 units of antitoxin per cubic centimetre?’ was 
coagulated at a series of temperatures—the coagulum at each temperature 
being filtered off before further heating. 
The following results were obtained :— 
Solids in each 
100 c.c. Antitoxic value. 
PRIME SOLU, 560.0. 0in-02 nae sucnemannae oud 9-4 grammes 400 
Filtrate after heating to 66° C. ......... Femi t ys 400 
. sas ite Eiko Mea i te 3°04 50 
; ie: (PS ne ers Beahbes 3 50 
