104 Messrs. Kanthack, Durham, and Blandford. 



The incubation period and the duration of the disease, as already 

 pointed out, are not entirely dependent upon the number of hsematozoa 

 in the material injected, or the source of the infective material. Thus 

 the haematozoa of lymphatic glands, &c., are as infective as those of the 

 blood. The duration of the disease is not materially affected by the 

 mode of inoculation adopted, and is about the same, whether the 

 infection was brought about by subcutaneous, intravenous, or intra- 

 peritoneal injection, or by a superficial scratch. 



Material taken from the bodies of animals twenty-four hours, or some- 

 times less, after death, is hardly ever infective, even when several cubic 

 centimetres are injected, so that we have no evidence of a resisting or 

 sporing form which survives in the tissues or blood of the dead animal, and 

 is inoculable into other mammals. It must be added that putrefactive 

 changes often set in with great rapidity in the bodies of animals dead 

 of nagana. 



Blood drawn from the living infected animal and kept in vitro in an 

 aseptic condition, retains its infective power at most for three or four 

 days, but this period is generally less. Complete drying also renders 

 blood non-infective. 



Blood heated to 50 for thirty minutes invariably becomes non- 

 infective, even in large doses (such as 4 c.c.), while when heated to 

 46 C. for half an hour it proved infective in one out of two cases, 

 although apparently the hsematozoa had become non-motile at least 

 no motile forms were detected under the microscope. But even in this 

 case the lethal period was not prolonged. 



Infection by feeding has been attempted by means of a number of 

 experiments. Sometimes it was successful, in most cases unsuccessful, 

 so that it has seemed to us that the possibility of infection by the 

 mouth depends on accidental lesions about the mouth, nose, ears (in 

 rats), or alimentary tract. 



Of a number of rats fed on organs of nagana animals, only a few 

 acquired the disease, and these invariably showed superficial lesions of 

 the snout and ears, due to lice. When fed upon infective material, 

 they bury their snouts in it as well as scratch their ears with their 

 blood-stained forepaws. Furthermore, in the rats which acquired the 

 disease through feeding, the cervical glands were always enlarged most, 

 which proves that the hsematozoal infection must have taken place in 

 the head, for, as we shall show, the primary infection travels by the 

 lymphatics. 



A cat fed repeatedly on soft tissues of the bodies of infected dogs 

 and cats, and subsequently on the bodies of dead rats, died at a time 

 corresponding by lethal period to an infection at the first meal on rats. 

 We regard it as probable that some splinter of bone caused a super- 

 ficial lesion through which the hsematozoa were enabled to enter. 



One rabbit, fed carefully by means of a pipette with large quantities 



