82 The Philippine Journal of Science ms 



tion of cysts and spores. The significance of this process is 

 not limited to spore formation, for with fertilization goes a 

 complete rejuvenescence of the organism — a renewal of its 

 vitality, which is not without its clinical significance. The busy 

 practitioner is prone to regard this phase of the life cycle as 

 leading up only to the infection of new hosts, and while this is 

 an important desideratum in regard to future hosts, it yet has 

 a very important bearing on the welfare of the original host. 



The belief is very current among protozoologists that proto- 

 zoa, like other animals, are endowed with a certain potential of 

 vitality that declines as the organism grows old. That is to 

 say, a protozoon passes through periods that we characterize 

 as youth, maturity, and senescence. With senescence the or- 

 ganism attains a degree of almost total protoplasmic stability, 

 and unless some revitalizing agency intervenes, it dies literally 

 of old age. In nature this rejuvenescence is brought about by 

 the process of fertilization, which seems to be universal through- 

 out the entire animal kingdom, and the organism issues from 

 it endowed with a new potential of vitality with which to cope 

 with the vicissitudes through which it must pass, which, in the 

 case of a parasite, are many. 



So it is with the coccidia. The organism passes through many 

 asexual generations, gradually exhausting its vitality. Perhaps, 

 also, there is the added burden of a declining food supply or 

 other unfavorable conditions. In other words, the vitality of 

 the parasite has become lowered, and it must have relief, else 

 it will die. 



To this condition the organism reacts by developing its prop- 

 agative or sexual phase, and once this has been initiated re- 

 infection of the original host becomes impossible except through 

 the original channels — autoinfection ceases. Gradually the schi- 

 zogonous or asexual cycle ceases, and the intracellular tropho- 

 zoites become gametocytes, after which stage they are incapable 

 of continuing the infection. The sexual phases develop, the 

 cysts pass out with the faeces, and in time, the host is completely 

 purged of its original infection though not necessarily immune 

 to subsequent infections. Here the necessity for fertilization 

 to restore the flagging vitality of the parasite has been met and 

 has operated to bring about the self -limitation of the disease; 

 spore formation has, in a measure, been incidental. 



May this not, in part, explain the lack of information on human 

 coccidial infections? Our information on the symptomatology 

 of human coccidiosis is very meager. Some of the writers speak 

 of diarrhoea, but there they stop. Chronic diarrhoea, unless 



