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



day only young parasites again were found, which represented a fifth 

 generation. No further development, however, occurred, as the conditions 

 in the culture were gradually becoming more and more adverse. We have 

 thus evidence that the parasites will, under very suitable conditions, actually 

 proceed in the original culture tube through four complete generations 

 without the medium being in any way renewed. 



We now wish to draw particular attention to several points of great 

 interest which occur in the cultures of P. falciparum,. In these there is 

 a definite tendency for the parasites to ' clump together into masses 

 immediately the circular mass of pigment appears, and even before segmen- 

 tation begins. This tendency to clump becomes more marked when 

 sporulation actually commences. In our opinion this phenomenon explains 

 the reason why sporulation occurs as a rule in the capillaries of the internal 

 organs. We seldom see sporulation or even presegmenting forms in the 

 peripheral blood of malignant tertian cases, and the phenomenon of clumping 

 explains this in a satisfactory manner. All the large parasites tend to get 

 caught in the fine capillaries of the internal organs, and thus only young 

 rings whose containing corpuscles have not yet acquired the clumping 

 tendency are seen in the peripheral circulation. This fact explains many 

 phenomena of pernicious malaria, and shows how comatose malaria may 

 occur in infections with P. falciparum. 



The Morphology o/P. falciparum in the Human Host. 



This is identical in every respect with that obtained in vitro, so that it is 

 hardly necessary to describe it in detail. As already stated only the young 

 ring forms of this parasite are found in the peripheral blood as a rule ; this 

 is due to the fact that when these parasites have grown larger than the ring 

 stage, the containing corpuscles stick together, forming clumps which are 

 unable to circulate, and thus are arrested in the fine capillaries of the inner 

 organs. The study of the further stages of this parasite is obtained by 

 examining smears of the inner organs such as the spleen, liver, brain, etc., of 

 cases which have died. The autopsy smears of over one hundred cases have 

 recently been examined by one of us (D. T.), in conjunction with Dr. W. M. 

 James, in Panama. En such smears one finds the parasite in different stages 

 of development. In some, presegmenters only are found ; some show only 

 young rings, and others only sporulating forms. This depends entirely on 

 the stage of development of the parasite at the time of the patient's death. 

 In some cases, of course, several stages of development are found, since one 

 patient may contain several broods of parasites which are in different stages 

 of development. In only one case did we find the parasites in the stage of 



