Aug. i, i93i Some Observations Regarding Eosinopliiles 681 
conclusions arrived at by many writers regarding the percentages of 
eosinophiles in the blood of normal horses or horses suffering from various 
diseases. Another fact that is apparently often if not always over¬ 
looked is the resistance of the animal. Weinberg and Seguin ( io ) 1 have 
pointed out that the eosinophiles possess specific attraction against 
certain toxic substances, especially those of parasitic origin. It would 
seem from this that if the resisting power of the animal were high the 
eosinophiles would be plentiful in parasitic diseases. If the resistance 
were low the eosinophiles would be few. 
In general it can be said that in the various species of animals the 
physiological functions of the leucocytes are essentially the same. If 
this be so, cattle must be very severely infested with parasites or else 
their resistance is high. Dimmock and Thompson (4) have shown that 
the average percentage of eosinophiles in the blood of normal cattle is 
* 3 * * 5 * Whatever the cause may be, it certainly presents a very inter¬ 
esting and important problem for further research. According to the 
tables given by Burnett (2) the percentages of eosinophiles are about 
the same for all animals excepting cattle. 
One thing that adds difficulty to the study of the blood in apparently 
normal animals is that nearly all are harboring more or less large numbers 
of parasites of various genera. Two apparently normal animals observed 
have presented a very high percentage of eosinophiles. No. 8 for 
nine examinations over a period of six months averaged 17.2 per cent of 
eosinophiles. O11 autopsy, this animal showed a relatively small number 
of internal parasites. No. 1 for one examination showed 13 per cent, 
and on autopsy there were found large numbers of internal parasites. 
As these were the only two animals that showed unusually large 
numbers of eosinophiles, very little more can be said about their presence 
as an aid to the diagnosis of internal parasites. One examination can 
be picked from some of the other cases that shows nearly as high a per¬ 
centage as did No. 1. Again, it can be said that results will be conclusive 
only as the observations are made over a period of time on the same 
animal. Then also, one must consider that for some cause the animals 
might become more severely infested with parasites, or else they might 
get rid of them. There is apparently some seasonal variation, especially 
in regard to the intestinal worms, more being present in the fall and 
winter than in the spring and summer. This also should be considered. 
1 Reference is made by number (italic) to “Literature cited,” p. 688. 
