296 BACTERIOLOGY FOR NURSES 



than half the diameter of a red blood corpuscle. The gametocytes 

 differ also in that they are crescentic in shape when first liberated 

 from the red blood cells. 



Methods of Examination. The organisms may be studied 

 in fluid or dried preparations. In the former case a drop of blood 

 from a pricked finger or ear lobe is allowed to fall upon a coverslip 

 and examined in a hanging drop, or the coverslip may be gently 

 inverted over a flat slide and the rims sealed with vaseline. Dried 

 preparations are made in the manner described for blood films 

 and stained with one of the special blood stains. 



Cultivation. In 1911 Bass and Johns announced that they 

 had succeeded in cultivating P. vivax and P. falciparum outside 

 of the body. The first cultures were obtained by defibrinating 

 blood taken from malarial patients. Growth of the parasites took 

 place within the red blood corpuscles in exactly the same manner 

 as in the human body so long as anaerobic conditions were main- 

 tained. Parasites transferred from tube to tube of defibrinated 

 blood were thus carried through several generations. 



Pathogenesis. Relatively little is known of the pathogenic 

 processes which occur in malaria. The organisms are not always 

 equally abundant in the circulating blood ; at certain stages they 

 tend to be more numerous in the internal organs. The spleen be- 

 comes enlarged. The liver and kidneys may also show some 

 swelling. It is definitely known that the occurrence of the fever 

 is coincident with the liberation of the merozoites, but whether the 

 increased temperature is due to a toxin liberated at the same time 

 is as yet undetermined. Since the organisms attack mainly the 

 red blood corpuscles the anemia which is so pronounced a feature 

 of the disease is readily explained : the parasite absorbs the cell 

 pigment and thus destroys its function. During the paroxysms 

 there is always a marked increase in the number of leukocytes, 

 followed by a rapid decline. An interesting feature of the disease 

 is the increased percentage of the mononuclear leukocytes, which 

 sometimes even outnumber the polynuclears. The cells become 

 particularly active phagocytes and engulf great numbers of pig- 

 mented parasites. In fact, the presence of excessive numbers of 



