200 PARASITISM 



Minchin suggests, it is possible that the organism is taken into the 

 digestive tract and the sporozoites liberated there to pass through the 

 epithelial cells into the blood, where asexual reproduction occurs. If 

 this questionable life history is true, it is conceivable that the ancestral 

 forms of the blood-dwelling hemosporidia were similar to coccidiidia 

 and made their way into the blood spaces from the digestive tract. 

 On the same hypothesis it is further conceivable that the blood-sucking 

 insects or leeches, while usually able to digest such forms taken in 

 with the food, in some cases provided a suitable environment for their 

 further development. Spore cases, characteristic of the supposed 

 ancestral forms, would be unnecessary with the substitution of the 

 insect-dwelling mode of life for the former exposed life, and, on 

 the other hand, would be of marked disadvantage to the young forms 

 upon reinoculation in the blood of a new r host. According to such an 

 hypothesis, the first or original primary host of such hemosporidia 

 would be man or other vertebrate type, while the secondary or "inter- 

 mediate" host would be the insect or leech. On such an hypothesis it 

 might be further assumed that in earlier times the intermediate host 

 acted as a mere carrier, the organisms remaining passive during the 

 interim. 



The above is the opinion concerning intermediate hosts held by 

 Minchin ('07) and other protozoologists whose dicta carry much 

 weight, but opposed to them are other students of the group, including 

 Laveran, Mesnil, Grassi, Liihe, and others whose conclusions, based 

 upon the recent observations on the blood-dw r elling forms, are more 

 convincing. Such conclusions are based largely upon the fact that the 

 most important phases in the parasite's life history occur in the diges- 

 tive tract of the invertebrate host, and that sporozoites, not merozoites, 

 are transmitted by them to man. Recent observations on blood- 

 dwelling forms in man indicate that the ancestral forms were not 

 coccidiidia but mastigophora. Schaudinn was the first to note the 

 relation between a free-swimming Trypanosoma noctuce in the blood 

 of the little owl, Glaucidium (Athene) noctuce, and the intracorpus- 

 cular parasite of birds which had been known as halteridium (hemo- 

 proteus); also, he was the first to see the transformation of the intra- 

 cellular into the flagellated form. Since then his observations have 

 been confirmed by various observers, the brothers Sergent ('C5) find- 

 ing most of the details as he had described them. In a number of 

 other forms as well the relation of a flagellated type to intracellular 

 types has been established. Rogers, Christophers, Leishman, 

 Patton, and others have noted the transformation of the intracellular 

 Leishman-Donovan bodies into flagellated parasites similar to the 

 genus herpetomonas, such transformation taking place both in the 

 digestive tract of the invertebrate host (Cimex rotundatus) and in 

 artificial culture media. From these observations there is reason for 



