PLASMODIA 65 



all the parasites present in the blood, and takes place shortly before 

 the commencement of a- feverish attack. For this reason, the life- 

 history of the malaria parasite is to be followed only by examining 

 specimens of blood taken at different stages of the disease. 



A species of Plasmodium which is valuable for purposes of com- 

 parison, or it may even be used for demonstration in place of the 

 malaria parasite, is Proteosoma prcecox, found in the blood of in- 

 digenous singing birds, though it is less frequent than Hcemoproteus 

 noctuce. It should be sought in sparrows, these birds being easily pro- 

 curable in large numbers. Frequency of infection varies with the 

 season and with the locality. Ruge found that from April to September 

 was the most favourable period in Berlin, nearly 30 per cent, of sparrows 

 being infected. Demonstration is rendered difficult by the fact that, 

 after a short acute stage of infection, the parasites become so few in 

 number that their presence cannot be proved by direct examination of 

 the blood, but only by inoculation of control birds. Proteosoma may, 

 however, be transmitted to canaries, and this factor is of considerable 

 .assistance in maintaining a stock of parasites once they have been 

 found. 



The developmental stages are shown in fig. 18. The differentiation 

 of the two sex-forms, both from one another and from the asexual 

 form, is similar to that observed in Hcemoproteus. The pigment 

 granules in the plasma also resemble those of Hcemoproteus and should 

 be examined in the same way. The maturing of the sex-form may also 

 in this case be watched under the microscope, but the Plasmodida do 

 not attain to the ookinet stage under artificial conditions. 



It will be sufficient for the present purpose to describe those 

 features in which the species vary and to which special attention 

 should be paid by the student. 



The Proteosoma of birds differs from the human malaria parasite in 

 that, shizogony not being synchronous, different developmental stages 

 may be observed in a single blood preparation. It manifests, moreover, 

 .a double nucleation similar to that of Hcemoproteus, having a large 

 principal nucleus which colours pale pink with Giemsa, and close to 

 it a smaller nucleus which stains a dark violet and which corresponds 

 to the flagellar nucleus of the Trypanosomes (fig. 19, b). At certain 

 developmental stages, Proteosoma are furnished with a flagellum 

 similar to that of the Trypanosomes (fig. 19, a and c). 



Of the human malaria parasites, the germ of malignant fever, 

 Laverania malarice, is distinguished from the others by its immature 

 sex-forms, which have a characteristic crescent shape, (fig. 17). The 

 benign tertian parasite (Plasmodium vivax, fig. 18) causes the affected 

 erythrocyte to swell until it becomes larger than the normal. It 

 forms 14 to 24 (generally 16) merozoites, and the entire developmental 

 5 



