54 
Annals of the Transvaal Museum. 
independent parasite genus of their own and that they were the cause of 
a definite disease, which had to be separated from redwater. I was, how- 
ever, until recently, unable to give this proof in such a way as would 
remove all doubts. 
Some years ago I sent ticks to England ( Boophilus decoloratus) which 
were infected with P. bigeminum. They produced the disease in London 
when placed on an ox, and this ox formed the starting point of many 
investigations and inocculation experiments undertaken in England. As 
a result of such investigations, Nuttall described the cycle of development 
of P. bigeminum in the blood, and according to this author, it is a simple 
division, as in the case of P. cams. He does not mention any forms 
corresponding to the coccus-like or marginal points mentioned . before. 
In Germany the disease haemoglobinuria of cattle was also investi- 
gated during the last few years : it was found to be due to a piroplasm 
which, owing to some slight difference, is considered to be a species of its 
own, and is called P. bovis , but it is very closely allied to P. bigeminum. 
No parasites resembling the peripheral coccus-like bodies were noticed in 
the life cycle of this parasite. 
Stockman and myself have carried out experiments for a number 
of years to immunize English cattle. The cattle were inoculated in 
England against South African redwater with the strain of redwater for- 
warded by means by the already mentioned ticks ; after the inoculation 
the animals were sent to the Transvaal to be exposed here. In the first 
lot of cattle exposed, I noticed the appearance of marginal points in the 
blood of two animals, which succumbed to the disease. A second lot of 
ten heifers, which were all immunized in the same way in London, were 
not exposed to natural infection after their arrival, but inoculated a 
second time in the Transvaal with blood containing P. bigeminum. The 
result was that this inoculation did not break the immunity against 
redwater. After a certain period, varying in length from twenty-seven 
to thirty-two days, a typical fever reaction commenced which was initiated 
and accompanied by the presence of marginal points. Of ten animals 
injected, five died. It was evident that P. bigeminum was* not responsible 
for this disease. With the inoculation of the blood two different parasites 
had been injected — P. bigeminum , against which the animals were immune, 
and another one, the marginal points, which caused the disease. If this 
conclusion was right, it had to be expected that it would be possible to 
separate these two parasites, at least to isolate the one with the shorter 
incubation time. It was, indeed, possible to do so with P. bigeminum , 
whose incubation period is the shorter one. A pure infection resulted 
after injections of blood, taken at the beginning of the acute attack of 
redwater, into a susceptible beast. When this animal, at a later period, 
was infected with marginal points it promptly reacted to this infection. 
The reverse experiment was not so easy, because wherever we had an 
infection with marginal points it was complicated with P. bigeminum , so 
that the inoculation of such blood would constantly cause redwater in the 
first instance. An observation I had made showed that animals imported 
from Aliwal North, although promptly reacting to redwater, did not do so 
to the injection of blood containing marginal points. I concluded, there- 
fore, that these animals are immune against this latter parasite. It had to 
be expected that when blood of such animals was injected into susceptible 
animals only marginal points would appear. This has been done in 
several instances, and in every one, after a typical long incubation time, 
marginal points alone appeared. After recovery, the animals were injected 
