54 -' 
This injection was repeated after an interval of a week. No 
increase of auto-agglutinin was found to occur in the animals 
blood. 
Another possible explanation for the cause of the development 
of auto-agglutinin is that it is formed by the animal mechanism 
as a direct response to the stimulus of the pathogenic agent. In 
the consideration of this question it is necessary to inquire whether 
auto-agglutinin alone is present in excess in infected blood ur 
whether we have at the same time a corresponding alteration in the 
iso- and hetero-agglutinin contents of the serum. 
Mention has already been made of the fact that in every case 
where the serum of an infected animal was found to possess the 
property of clumping its own erythrocytes to a considerable degree, 
it also agglutinated markedly those of other members of the same 
species. 
It was further observed that the plasma of infected animals 
frequently appeared to agglutinate the red cells of animals 
belonging to different species to a greater extent than normal. The 
case of human trypanosomiasis already referred to presented an 
excellent example of an increased capacity on the part of an 
infected serum to agglutinate foreign erythrocytes. 1 he serum of 
this case clumped the red corpuscles of rats, guinea-pigs and 
rabbits in a remarkable manner. A few drops of the inactivated 
serum when added to an equal volume of the blood of one of these 
animals caused intense agglutination in a few seconds at room 
temperature. The action of normal human sera on these corpuscle* 
was much slower and did not approach that of the former ' n 
intensity. 
Experiments were undertaken with the object of comp arin *f 
quantitatively the auto-, iso-, and hetero-agglutinin in the blood o 
several infected animals with that existing in the blood of normal 
animals of the same kind. 
Technique .— T he method adopted was that previously used f° 
comparing the amount of auto- and iso-agglutinin in ; ' 1L 
defibrinated plasma separated from the red cells at 37° C- "' t!l 
that present in the serum obtained from blood which had clotted 
at o° C. 
Inactivated defibrinated plasma was prepared from norm?' 
