528 PROTOZOAL DISEASES. 



periods (say, when the temperature is 103° F. or over) ; and surra will 

 always ensue after inoculation with blood containing it. These minute 

 trypanosomes may, during an exacerbation, be seen by the aid of a micro- 

 scope, in vast numbers, traversing with great activity every drop of blood 

 examined. They are said to attack and destroy the red corpuscles, and 

 thus directly interfere with the nutrition of the body. When the acute 

 stage has passed, these roving organisms disappear from the blood ; the 

 temperature falls ; and there is an interval of apparent health. They are 

 so tenacious of life, that, unless under special and very exceptional treat- 

 ment, the sufferer, after passing through a more or less prolonged course 

 of crises and intermissions (Steel has observed as many as seventeen), finally 

 dies of exhaustion, and from the diseased changes in his system, to which 

 the malady has given rise. 



Under the microscope, the presence of these parasites in a drop of blood, 

 is indicated by an irregularly intermittent and characteristic quivering of 

 some of the red corpuscles, which are much altered in form ; although the 

 white ones remain unchanged in appearance. After a further and careful 

 examination of this " slightly quivering blood, we may at length see a 

 minute thread-like organism, with eel-like movements, emerge from the 

 mass of corpuscles and move slowly forward, or we may observe the little 

 being tugging, with all its' might, at a red corpuscle, endeavouring to 

 detach it from its rouleau " (Sted). The parasite is about ^th of the 

 diameter of a red corpuscle in thickness, and is from three to six times its 

 length. It seems to have a thick body and a spiral tail. 



MANNER AND TIME OP INVASION.--It appears from the investiga- 

 tions of Lingard that this microbe, perhaps in another form, can liva in 

 water outside of the animal body. In the Bombay Presidency it has been 

 found in the blood of a large proportion of rats and bandicoots, the health 

 of which rodents it affects but little. Stagnant water and grass growing 

 on lately inundated land, form favourable resting-places foT the host. 

 Tabanida; and glossina flies act as carriers of surra from infected horses 

 to sound ones, in the same way that nagana (p. 530) is transmitted by the 

 Tsetse fly. This kind of fever is incapable of being transmitted, under 

 ordinary circumstances, from one animal to another, except by inoculation. 



Although cases of surra may be met with all through the year, its 

 microbes are particularly active during the rainy season. When outside the 

 animal body and in a dry state, they are killed or rendered inert by pro- 

 longed atmospheric heat. 



THE PERIOD OF INCUBATION seems to be liable to great 

 variations. It may be put at 6 or 8 days after inoculation or 

 ingestion of blood taken from an animal suffering from surra. It 

 appears from Lingard's investigations that the period of latency 

 may be prolonged to 13 days, if the blood used for the inoculation 

 has been taken from the dead animal ; and that when the parasites 

 have been given in water by the mouth, symptoms of stu-ra may 

 not appear for even 75 days. We have no exact data to determine 

 the time required for the disease to become manifest, under natural 

 conditions. 



DURATION OF THE DISEASE.— Gunn states that the average 

 duration of the disease is about 52 days. 



LIABILITY AND CHANCES OF RECOVERY.— Horses, mules, 

 donkeys, cattle, dogs, elephants, monkeys, camels, and other 



