Kauthack, Durham and Blandford found that Guinea pigs were more resistant than rabbits, surviving the inoculation for a longer time. Bruce also found the native South African sheep and goats more refractory than others, yet their hæmatozoön was as deadly to other animals as that of horse or dog. Pigeons and South African hens proved refractory. Manifestly in Africa the present races of some animals are the products of the survival of the fittest.
Inoculation. The disease has been produced experimentally by inoculation only. Feeding experiments on rabbits, cats and Guinea pigs, the sucking by puppies of an infected dam for 14 days, coitus, and even the careful dropping of infected blood under the eyelid failed to convey it. Lousy rats with sores on face, one cat doubtless scratched by a bone, and one rabbit supposed to be infected by sexual congress (Rouget) offer exceptions, which in the light of the general results must be looked on as probable inoculations through wounds.
Successful inoculations were made with blood, lymph gland, spleen, bone marrow, aqueous humor, serum, œdema fluid, and testicular juice. The effectiveness of inoculation did not vary materially with the different fluids used, with the amount, nor with the point selected for its insertion, subcutaneous, intravenous, intraperitoneal, or on a mere scratch.
Virulence is lost in the dead body in 24 hours or less; when the infected blood is kept aseptically in vitro, in 3 or 4 days at most; or when completely dried. Heating to 122° F. for 30 minutes sterilized, while at 114.8° F. for half an hour the trypanosoma became nonmotile, but not quite non-virulent.
Symptoms. Hyperthermia is marked about the time of the appearance of the infusoria in the blood. (Horse 106.7°; dog 104°; rabbit 105.8°), and in the horse there was a paroxysm with each new swarm of the parasite. In one ass intermissions were not observed. In rabbits there was no constant ratio between the temperature and hæmatozoa, hyperthermia was constant or nearly so. The horse had marked hyperthermia up to death, dogs and cats showed a marked descent even to subnormal, before death.
Anæmia is a marked feature the red globules being greatly reduced, and they show a tendency to clump in masses instead of forming rouleaux. The serum added to healthy blood has the same effect on that. Leucocytosis is not constant nor excessive (15,000 to 34,000 per c.m. at the highest). In clotting the blood may form a buffy coat.
Œdema is common in horse, rabbit, cat and dog especially about the head, legs, belly and genital organs. Rabbits often show swellings, excoriations and sores of the labia, prepuce and penis favoring inoculation by this channel.
Conjunctivitis is common in cats, dogs, rats, rabbits, often in connection with facial œdema, and corneal opacities and ulcers, and turbidity of the aqueous humor may follow.
Nasal catarrh often interferes materially with breathing.
Muscular wasting and debility are prominent phenomena, especially in horse, dog, cat and rabbit, the loss of weight reaching 20 or 30 per cent.