SERUM THERAPEUTICS. 
489 
furnish the anti-toxin serum of tetanus and diphtheria. He is 
not very sensitive to the diphtheritic virus, but the serum can 
be readily obtained in large quantities by bleeding from the 
jugular vein, and, besides, this serum has proved to have a 
strong anti-toxic power. Of course he must be free from any 
disease, and glanders must be eliminated by injections of 
mallein. For diphtheria, the cow, dog, sheep, goat and rabbit 
can also be used. The cow is very sensitive to the diphtheritic 
poison, even fatally so'; the toxin is excreted with the milk. 
Formation of the Anti-toxin— The anti-toxin is a cellular 
secretion, but it is not determined which set of cells are active in 
this process. It is not a transformation in the body of the 
toxin injected. The-anti-toxin diminishes with the cessation of 
the toxin injections. In one experiment, two rabbits were 
each injected with 103 cc. of tetanus toxin, the first in 33 daily 
doses, the second in 9 larger doses. The serum of the first 
neutralized 150 parts of tetanus toxin; that of the latter only 
25 parts. The two serums were of unequal preventive power; 
the quantity of toxin injected was the same in both cases but 
the method of administration differed. By successive bleed¬ 
ings in the rabbit, a quantity of blood equivalent to the entire 
volume of the circulation can be removed and anti-toxic power 
of the blood is not sensibly lessened. The anti-toxin is secreted 
rapidly as it is drawn away without any new injections of 
toxin. 
An important question is the manner of action of the anti¬ 
toxin after the introduction into the body. In diphtheria and 
tetanus it counteracts the effects of the toxin; in some diseases 
it is protective only against the microbe and such animals as 
remain as sensitive to the toxin as those which are not im¬ 
munized. 
A mixture of anti-toxin with an immunizing power of one 
billion, and tetanus toxin one one-thousandth cc. of which de¬ 
stroys a mouse, in proportion of 1 to 900 becomes harmless. 
One-half cc. (one eighteen one-hundredth cc. serum) injected 
into a guinea-pig does not produce tetanus. This result, how¬ 
ever, is not always the same; a mixture innocuous to mice is 
fatal to guinea-pigs. In eight out of ten guinea-pigs one-half 
