232 
Haematozoa 
from various kinds of leuchaemia. None of these animals showed 
any deviation from health or signs of parasites. 
There is another blood change in nagana which on the whole is best 
seen in the rat when in an advanced stage of the disease. This change 
is manifested by a change of colour of the blood from the brilliant scarlet 
to a dull purplish or chocolate colour. The contrast between the healthy 
blood and the diseased blood is very striking when it is kept from coagu¬ 
lating by means of citrate, and can be recognised at a distance of some 
yards. In the clotted condition the phenomenon is likewise apparent, 
though hardly so marked. This dull coloured blood maybe shaken with 
air, or allowed to stand for a week or more without developing the full 
red of normal oxyhaemoglobin. By the addition of the diseased blood 
to healthy blood the colour of the mixture is more or less dulled, 
so that the presence of healthy haemoglobin is not capable of causing 
a discharge of the abnormal colour. Examination with the spectroscope 
showed the bands of oxyhaemoglobin. Dr F. G. Hopkins kindly 
examined a specimen and considered that the oxyhaemoglobin bands 
did not appear quite normal. Dr Haldane has kindly drawn my 
attention to some observations 1 on the blood colour in poisoning with 
nitrobenzol derivatives. It appears that some species exhibit such 
changes whilst others do not do so ; thus nitrobenzol causes no blood 
colour change in mice, though it does in dogs and cats. With dinitro- 
benzol the blood of the rabbit becomes chocolate coloured ; this seems in 
part due to the presence of methaemoglobin but some other abnormal 
pigment is also probably at work. 
Considerations such as these lead to the thought that though we 
now know much of the life-history and morphology of the parasites, 
this knowledge has taught us little, if indeed anything, concerning the 
disease itself. The same may be said of malaria in which morphology 
has not availed to advance our knowledge beyond diagnostic and 
preventive measures, the real nature of the disease and its symptoms 
yet remain to be unfolded. Another blood change, which may be 
mentioned as a matter requiring further elucidation, was noted in 
nagana-cachectic rabbits and consisted in the comparative resistance 
to haemolysis by the quillaia saponins. These saponins (sapotoxin and 
quillaiic acid) are capable of haemolysing red blood corpuscles in high 
degree, the extent varying in different species of animals. If 1 °/o 
ddutions of normal blood are treated with the glucosides it is found 
1 Haldane, Makgill and Mavrogordato, Journ. of Physiology , xxi. Nitrobenzol and 
dinitrobenzol, p. 184. 
