W. L. Yakimoff and others 
59 
Characteristic. Leucocytosis of very long duration—the longest. Leuco- 
cytolysis. Lymphocytosis. Decrease in percentage of the polynuclears. 
Arneth index continues “ shifting to the left.” Continued fall in the 
number of red blood corpuscles, percentage of haemoglobin and alkalinity. 
Gradual rise of the colour index above 1. Narrowing of the correlation between 
the white and red blood corpuscles. Periodical appearance of trypanosomes 
in the blood. 
This period may be called the 'period of greatest leucocytosis and lympho¬ 
cytosis. 
Third period. Several days preceding death. 
Characteristic. Change in the increased and decreased number of leucocytes, 
terminating in the secondary—small—leucocytosis. Leucocytolysis. Second 
polynucleosis. Decrease in the percentage of lymphocytes. Arneth index 
continues “shifting to the left.” Decrease to a minimum in the number of 
red blood corpuscles, the percentage of haemoglobin and the alkalinity. 
Continued rise of the colour index and a narrowing of the correlation between 
the white and red blood corpuscles. Periodical appearance of trypanosomes 
in the blood. 
This period may be called the period of the second leucocytosis and poly¬ 
nucleosis. 
Thus, the vital phenomena in the blood of the horse during experimental 
infection by trypanosomes are similar to those in dogs, with the difference, 
however, that in dogs the second period is characterized by leucopaenia, and 
in horses, on the contrary, by leucocytosis. 
We shall try to consider these phenomena separately. 
As was to be expected, the toxin produced by trypanosomes evokes an 
anaemic effect. The number of red blood corpuscles and amount of haemo¬ 
globin decrease. 
The haematogenous organs are obliged to work intensely in order to 
supplement this deficit, and, therefore, we find in the peripheral blood normo¬ 
blasts and polychromatophils (which some authors take for young red blood 
corpuscles), jlowever, this struggle proves to be above their power—and 
toward the end of the life of the animal the number of red corpuscles and the 
percentage of haemoglobin fall. 
The effect produced by this trypanosome is similar to that of the 
other trypanosomes studied in this respect (Trypanosoma brucei, T. equinum, 
T. evansi, T. equiperdum). 
On taking up the work with the white blood corpuscles, we expected to 
meet with phenomena similar to those in dogs, in which (according to 
Yakimoff, Levi della Vida and C. Verdozzi), after a brief leucocytosis, during 
the whole period of infection and nearly till the very death, leucopaenia was 
observed. Instead of this, we see that the dominating phenomenon is leuco¬ 
cytosis. This phenomenon indubitably presents a reaction of the organism 
against infection. 
