DIPHTHERIA. 305 



of antitoxic serum seems to bear a distinct relation to 

 the age of the serum, fresh serums being more liable 

 to produce it than those which have^been kept for a 

 month or two. 



I have found that the "keeping" qualities of the se- 

 rums, when properly preserved, are of long durati6n. 

 Samples examined two years after having been exposed 

 for sale in the markets have been found unchanged. 

 The serums most prone to deteriorate seem to be those 

 of highest potency, but even here the good qualities are 

 unchanged for months. 



Freezing is without effect and ordinary temperature- 

 changes are harmless to the serum. The antitoxic power 

 is destroyed at 72 C., the point at which the serum 

 coagulates. 



The erythemata are probably in some way associated 

 with the globulicidal action of the blood. Keeping the 

 serum " until it is ripe " lessens this effect. The serums 

 from different horses probably vary much in both their 

 irritant and globulicidal properties, so that antitoxins 

 prepared by mixing the serums from a number of horses 

 are probably preferable to those from single horses. 



Dried serums are much less active than fresh ones. 



For purposes of immunization smaller doses than those 

 used for treatment suffice. According to Biggs, 2 cubic 

 centimeters are sufficient to give complete protection. 

 The immunity that results from the injection is of a 

 month or six weeks' duration. 



The transitory nature of this immunity is probably 

 dependent upon the fact that the antitoxin is slowly ex- 

 creted through the kidneys. 



20 



