164 
MALARIA 
ability to penetrate the tissues in passage to 
a blood vessel, if not directly introduced 
therein. This is confirmed by the infections 
resulting from the application of infected 
mosquitoes to blisters (Boyd and Stratman- 
Thomas 1934c). It is not known whether 
the crushing of an infected anopheline on 
the skin might result in infection. 
Artificial inoculations may be ranked in 
order of increasing reliability as subcu¬ 
taneous, intramuscular and intravenous. 
The first two methods are not only highly 
unreliable, but if successful are followed 
by long incubation periods. It is difficult 
to understand how trophozoites introduced 
by either of the first two routes make their 
way to the blood stream. Entirely apart 
from the dosage of trophozoites introduced, 
the duration of the incubation period or 
even the success of the inoculation follow¬ 
ing intravenous inoculation may depend on 
whether the blood of the donor and re¬ 
cipient are compatible or incompatible 
(Polayes and Derby 1934). These observ¬ 
ers report mean incubations, presumably 
of vivax, of 4.3 days when the bloods are 
compatible and of 8.2 days when they are 
incompatible. The injection of incom¬ 
patible blood soon gives rise to an elevation 
of temperature, chills, nausea and dyspnoea. 
The necessity of typing in order to avoid 
this reaction can be avoided by effecting 
inoculation with not over 10 cc quantities 
of blood. 
We are likewise ignorant of the minimal 
number of trophozoites of the parasites of 
man which can initiate infection, although 
Coggeshall (1938a) found that in Macaca 
mulatto, a single trophozoite of the highly 
virulent P. knowlesi could induce infection. 
Stauber (1939) working in Huff’s labora¬ 
tory has successfully initiated an infection 
with P. cathemerium by the inoculation of a 
canary with a single merozoite. We have 
effected inoculations of P. vivax with as few 
as ten trophozoites on intravenous inocula¬ 
tion, and are of the opinion that the number 
might still be further reduced. Distinction 
of the age of the trophozoites must be made, 
as an inoculation effected with 10 preseg- 
menters would have a different significance 
from one effected with 10 young amoeboid 
forms. 
The possibility of a malarial infection 
occurring in the recipient of a transfusion 
from a donor with a latent infection is 
always a matter of concern to a surgeon, 
although if this possibility is borne in mind, 
and blood smears are taken from the re¬ 
cipient in the event a pyrexia develops, 
there is little actual risk. Infected donors 
usually have latent infections, with parasite 
densities so low that the recognition of the 
infection by microscopical examination is 
hopeless. Consequently surgeons should 
avoid, or at least regard with suspicion, 
donors for direct transfusions who have 
resided in endemic regions, or give a his¬ 
tory of past malaria infection (Hutton and 
Shute 1939). An instance has even been 
reported where, on direct transfusion, the 
recipient infected the donor. While all 
species of parasites may be encountered in 
this connection, the extreme and unpre¬ 
dictable duration of latent quartan infec¬ 
tions makes them an especial hazard. 
Malarial infections also merit considera¬ 
tion in connection with the growing prac¬ 
tice of storing blood under refrigerated 
conditions for emergency transfusions. 
Johns (1931) succeeded in infecting paretic 
patients with defibrinated blood containing 
1 per cent dextrose which had been stored 
at 0° C for 16-18 days. Since these condi¬ 
tions closely coincide with those used on 
blood destined for storage, malarial trans¬ 
fer might be a possibility, although the use 
of citrate as an anticoagulant would be 
detrimental to the parasites. 
Assuming that the route of inoculation 
is adapted to the parasite, an infection or 
take will follow their introduction. If the 
patient presents some degree of immunity, 
the infection may be of short duration and 
even remain subclinieal in degree. When 
an infection is artificially induced by intra¬ 
venous inoculation with the donor at the 
bedside, and the volume regulated by the 
degree of the donor’s parasitemia, some 
degree of take is almost inevitable unless 
the recipient is a refractory hyperimmune. 
On the other hand greater uncertainty fol- 
