TAXONOMY OF HUMAN MALARIA PARASITES 
23 
compact and bear a close resemblance to P. 
ovale. The nucleus and vacuole are well 
defined. Multiple infections of the red cells 
are common; band forms are absent. The 
older parasites are compact and exhibit a 
well defined vacuole. The pigment is yel¬ 
low-black and is not clumped. The “quar¬ 
tan-like ’ ’ gametocytes are pale in color with 
well-distributed pigment, the females being 
markedly different from those of P. vivax. 
There is little cell margin around the full 
grown parasites. The merozoites range 
from 10 to 12 in number. The host cells 
are always enlarged after the parasites are 
more than one-quarter grown and this en¬ 
largement may surpass anything seen in P. 
vivax infections. A faint stippling, finer 
than Sehiiffner’s dots, is sometimes present. 
Relapses are frequent even under intensive 
quinine and atabrine treatment, each attack 
resulting in heavy infections. 
Wenyon (1941) is of the opinion, in 
which we concur, that although this is an 
unusual parasite the full proof of its spe¬ 
cificity is still to be demonstrated. 
In view of the conflicting evidence and 
opinions, it seems that before rejecting or 
accepting any of the above types it would 
be expedient to follow the successive life 
cycles through both the human and the 
invertebrate hosts under controlled condi¬ 
tions. The practice of malaria therapy 
allows for such a procedure. 
Strains or Races 
It is generally recognized that within the 
morphological limits of the species of ma¬ 
laria there are numerous strains or races. 
These minor groups are now recognized on 
the basis of studies dealing with clinical 
virulence, infectivity to man and mosqui¬ 
toes, response to antimalarial drugs, and 
antigenic response. With better staining 
technique it may be possible later to corre¬ 
late these immunological differences with 
now unrecognized morphological characters. 
The rise of malaria therapy gave oppor¬ 
tunity for the systematic study of these 
strains of human malaria under controlled 
conditions and much data of practical im¬ 
portance have been accumulated both in 
this country and abroad. 
In this country various strains have been 
isolated and studied for varying lengths of 
time. The discussion here will be limited 
to those that are well established. 
McCoy strain of P. vivax. This strain of 
human malaria has been intensively studied 
by Boyd and his associates. It was secured 
in 1931 from a patient living near Talla¬ 
hassee, Florida, and has been maintained 
at the Florida State Hospital since that 
time. Up to August 1, 1939 (Boyd 1940a), 
this strain had been maintained through 47 
consecutive human-anopheline passages in¬ 
volving approximately four hundred pa¬ 
tients. This strain produces attacks of 
more than average severity, is a consistent 
gametocyte producer, and relapses are 
frequent. Boyd also shows this strain to 
be immunologically distinct when tested 
against four other strains: the White, the 
Wilson Dam, the Mayo, and the Cuban. 
Cleveland strain of P. vivax. To our 
knowledge this is the oldest strain of tertian 
malaria now maintained in the United 
States. We are indebted to Dr. H. N. Cole 
of the Cleveland City Hospital for informa¬ 
tion on this strain. He reports that it was 
obtained from a patient in 1925 and has 
been propagated since that time entirely by 
blood inoculation. The strain has been 
passed through from 1,500 to 1,800 patients 
during the 15 years without loss of viru¬ 
lence. 
The St. Elizabeth strain of P. vivax. 
This strain was obtained from St. Eliza¬ 
beth’s Hospital in Washington, D. C., in the 
spring of 1937 and has since been kept 
under continuous observation at the South 
Carolina State Hospital. It has occasion¬ 
ally been passed through mosquitoes but 
ordinarily it is transferred by the intrave¬ 
nous inoculation of 5 cc. of infected blood. 
When this strain and the U. S. Public 
Health Service quartan strain were intro¬ 
duced simultaneously in paretics, the vivax 
parasites usually dominated so that the ma- 
lariae parasites disappeared from the blood 
stream (Mayne and Young 1938). Up to 
December 15, 1940, this strain had been 
carried through 39 consecutive serial pas¬ 
sages involving approximately 94 patients. 
It ordinarily produces at least 20 parox- 
