1. Trypanblau promises to be an efficient remedy for bovine piroplasmosis, since it exerts a direct and obvious effect upon the parasites.

2. The effect of the drug upon Piroplasma bovis is similar to that which it produces upon the canine parasite. The dividing forms are the first to disappear, and after a few hours the pyriform parasites also disappear from the peripheral circulation; the parasites which are detected in the blood after a few hours appear degenerated and rounded or irregular; within nine to 45 hours or less all the parasites have disappeared from the blood.

3. As in canine piroplasmosis the disappearance of the parasites from the blood may be temporary. The parasites also disappear and reappear in small numbers (after two to 11 days) in animals undergoing natural recovery. In three treated animals the parasites reappeared in exceedingly small numbers after five to six days; in two they had not reappeared after 16 and 18 days respectively. The animals show no symptoms and progress towards recovery.

4. It remains to be detercnined (1) how long the blood of treated cows may contain parasites after the apparent recovery, (2) if the parasites in such recovered animals are altered in virulence, (3) if the parasites are capable of infecting ticks.

5. The experiments were conducted on nine cows, of which four served as controls and five were treated with trypanblau. Of the controls two suffered from haemoglobinuria, and one of these died of piroplasmosis; the two other controls had no haemoglobinuria and were very mild cases. All of the treated cows had haemoglobinuria and recovered. In four of the treated cows haemoglobinuria occurred before treatment began.

6. As might be expected, the drug exerts a more rapid effect when injected intravenously. The parasites disappear more slowly after subcutaneous injection of the drug. (Judging from our recent experiments on dogs, the giving of the drug per os promises to be without effect. See This Journal, p. 231.)

7. Although doses of 150–200 c.c. of a saturated watery solution of the dye were used, it is probable that smaller doses will prove efficient. The drug appears to produce no ill-effects upon cattle.

8. The drug, being a dye, has the disadvantage of colouring the tissues, more especially the subcutaneous connective tissues. How long the colouration persists remains to be determined. In any case this disadvantage can scarcely weigh in the balance as against saving the life of the animal, especially when used for breeding purposes.

9. We hope that experiments, which are about to be conducted in the field in Africa and elsewhere, will demonstrate the value of the remedy in practice.

10. Trypanblau and similar drugs should be given a trial in the treatment of Carçeag in sheep and Biliary Fever in horses.