61 
We believe that these morphological alterations do not explain the 
mechanism of anaphylaxis. It is probable that the mechanism will 
not be unraveled until further light is shed upon the chemistry of 
protein metabolism. 
Cases of sudden death in man. — Our experiments demonstrate that 
the horse serum used in cases followed by sudden death is no more 
toxic for guinea pigs than antitoxic horse serums used extensively in 
human therapy without untoward symptoms. 
It is our belief that it is not the special toxicity of the horse serum, 
but the sensitization of the patient, which accounts for the collapse 
or sudden death sometimes following the injection of horse serum. 
We are still unable to account for the ways in which man may be 
sensitized to a foreign protein. It seems perfectly plain, however, that 
man may be so sensitized. 
In previous publications we suggested that the essential lesion of 
serum anaphylaxis is probably localized in the respiratory center, 
and the association of asthma and hypersusceptibility to horse serum 
in man seems to lend some weight to this hypothesis. 
The knowledge of the fact that an injection of horse serum into 
some asthmatics may be attended with danger should be considered 
in the use of antitoxin. 
The repeated injections of small amounts of horse serum sensitizes 
guinea pigs. 
Repeated injections of large amounts render guinea pigs partially 
immune. 
Repeated injections of small amounts of serum into sensitized 
guinea pigs have no appreciable effect. 
Sensitized guinea pigs can not be immunized by repeated injections 
of heated serum (100° C. for one hour). 
We suggest a possible relation between the toxemias of pregnancy 
and anaphylaxis. 
Guinea pigs can not be sensitized with guinea-pig fetal blood. This 
shows that the fetal blood of the guinea pig does not contain an alien 
protein for the mother. 
Guinea pigs may be sensitized and subsequently poisoned with 
guinea-pig placental extracts. 
