1/2 THE ANIMAL PARASITES OF MAN 



incubator kept at a temperature of 37 C. to 41 C. The blood cor- 

 puscles soon settle, leaving a column of serum at the top, to the extent 

 of about half an inch in each tube. The leucocytes need not be 

 removed by centrifugalization. ]. G. Thomson (1913) and his 

 collaborators did not find it necessary to destroy the complement in 

 the serum, and they found that the malarial parasites developed at all 

 levels in the column of corpuscles, and not merely on the surface 

 layer of the corpuscles as first stated by Bass and Johns. 



So far only the asexual generation of the malarial parasites has 

 been grown in vitro. Thomson rarely observed haemolysis in the 

 cultures. Clumping of the malignant tertian parasites occurred. 

 In cultures of the benign tertian parasite (Plasmodium vivax) clumping 

 was not observed. J. G. and D. Thomson consider that this 

 difference as regards clumping explains why only young forms of 

 malignant tertian are found in peripheral blood, as the clumping 

 tendency of the larger forms causes them to be arrested in the finer 

 capillaries of the internal organs. It also explains the tendency to 

 pernicious symptoms, such as coma, in malignant tertian malaria. 

 Further it was found from cultures that P. falciparuni was capable 

 of producing thirty-two spores (merozoites) in maximum segmenta- 

 tion, while P. vivax produced sixteen spores (merozoites) as a rule, 

 though the number might be greater than sixteen. (Quartan parasites 

 produce eight spores or merozoites in schizogony.) 



It may also be mentioned here that Babesia (Piroplasnia) canis has 

 been successfully cultivated in vitro by Bass's method. This has been 

 accomplished by Thomson and Fantham, 1 Ziemann, and Toyoda in 

 1913. J. G. Thomson and Fantham used the simplified Bass technique 

 recorded above, namely, infected blood and glucose, incubating at 

 37 C. In one of the B. canis cultures, starting with heart blood of a 

 dog containing corpuscles infected with one, two, or, exceptionally, 

 four piroplasmata, Thomson and Fantham succeeded in obtaining a 

 maximum of thirty-two merozoites in a corpuscle. The cultures are 

 infective to dogs and sub-cultures have been obtained. 



Family. Piroplasmidae, Franga. 



The parasites included in this provisional family or group belong 

 to the Haemosporidia. They are minute organisms, sometimes 

 amoeboid, but usually possessing a definite form. They are endo- 

 globular, being contained within mammalian red blood corpuscles, 

 but they produce no pigment. The true Piroplasmata, belonging 

 to the genus Babesia, destroy the host corpuscles, setting free the 



1 Annals Trap. Med. and Parasitol., vii, p. 621. 



