80 



Messrs. J. G. Thomson and D. Thomson. 



observed in wet films, as smearing of the blood tends to break up the 

 clumps. No tendency to clumping occurred in our benign tertian cultures. 



Resistant Forms of Parasites. 



Sometimes it will be found that the parasites do not grow well in vitro. 

 They may only grow partially, stopping short of segmentation. This is 

 liable to occur if quinine has been given to the patient before the blood is 

 drawn. In other cases, only a few of the parasites reach maturity, these, 

 apparently, being able to resist successfully adverse conditions in the culture 

 tube. 



The Morphology of Plasmodium falciparum in Culture. 



The blood examined before incubation always showed the typical small 

 ring parasites of malignant tertian malaria ; these varied in size, with a 

 maximum diameter of about 3 fx. There was no enlargement of the red 

 blood corpuscles, and no Schuffner's dots. Fig. 1 (Plate 10) shows a small ring 

 parasite from the peripheral blood before incubation. After many experi- 

 ments in Liverpool, it has been found that there is great variation in the 

 rate of growth of P. falciparum in artificial media, and many suggestions 

 can be offered to explain this phenomenon. J. G-. Thomson and S. W. 

 McLellan (1912) found in one case that maximum sporulation of 

 P. falciparum occurred in 25 hours. This culture was made from a case 

 with very heavy infection of parasites, and the patient had taken no 

 quinine. The temperature of the incubator was only 38° C, but the glucose 

 added was slightly in excess of that recommended by Bass (1912). The 

 rapid segmentation of the plasmodia in this case, therefore, may have been 

 due to two causes : (1) the age of the parasites when introduced into the 

 culture tube, since it is to be noted that they were fairly large rings about 

 3 fx in diameter, and (2) the quantity of glucose may in some way have 

 hastened the growth. In other experiments, however, where the glucose 

 was slightly in excess, there was no such rapid growth, so that in all 

 probability the real cause of the rapid segmentation of the parasites in vitro 

 is due to the age of the plasmodia when drawn for incubation purposes. 

 Another factor which seems to influence the rate of growth is the previous 

 administration of quinine, and this may, in fact, inhibit the growth entirely. 

 On several occasions we have made unsuccessful attempts to cultivate the 

 malignant tertian parasite, and these have usually been from patients to 

 whom quinine had been administered. 



On two occasions complete sporulation did not take place till after 

 50 hours' incubation at -il C. On one of these occasions the parasites 

 completed several generations, as illustrated by the accompanying coloured 



