2 PROTOZOA AND DISEASE 



understand any pathogenic protozoa that have hitherto escaped 

 recognition. 



A perusal of even the following brief notes, from which many 

 points are necessarily omitted, will show that steady progress has 

 been achieved in the pathology of tropical diseases, amongst which 

 the foremost place must be reserved for malaria. 1 



We are indebted to Schaudinn for making our knowledge of the 

 protozoa of malaria more nearly complete. Among other points he 

 has explained the occurrence of relapses, such as may occur after a 

 long interval, when the disease has apparently been cured. Such 

 relapses appear to be brought about by female gametocytes, or 

 ' sporonts.' These females outlive all other forms of the parasite 

 in the human host, and when the resistance of the latter is lowered, 

 whether from intemperance, exposure to cold, or some other cause, 

 parthenogenetic multiplication of the parasites occurs. The Partheno- 

 genesis is described as follows : ' The nucleus of the gametocyte divides 

 into two parts ; one is rich in chromatin and stains deeply, while 

 the other is pale and stains feebly. The body becomes partially 

 constricted into two parts, one consisting of denser protoplasm, with 

 most of the pigment and the pale nucleus. This portion of the body, 

 with its contents, is ultimately abandoned as residual protoplasm ; 

 the other portion has lighter protoplasm and less pigment, and 

 contains the darker nucleus. This portion proceeds to sporulate, 

 as in the schizogony, and produces a number of merozoites, which 

 attack red blood-corpuscles, and give rise to a fresh endogenous 

 cycle, and consequently a relapse of the fever.' 2 



The more salient features of recent contributions to our know- 

 ledge of other tropical diseases, such as sleeping-sickness, kala-azar, 

 splenomegaly, and Delhi boil, are given in Chapter IV. of this 

 volume. What promises to be an elucidation of beri - beri has 

 been published more recently. 



1 When we speak of malaria as a tropical disease it should be with a mental 

 reserve to the effect that the disease was once common in the fens of our own 

 country, and the disease is still by no means limited to the tropics. 



2 E. A. Minchin, article 'Protozoa' in Allbutt and Rolleston's 'System of 

 Medicine,' vol. ii., part. ii. 



