IX8ECT AXD MULTICELLULAR PARASITES. 85 



in many rats by feeding them bread which had 

 been mixed with crushed infected mites. The in- 

 testinal juices of the rat break up the sporocyst. 

 and set free the sporozoites, which as "vermicules" 

 penetrate to the veins and lymphatics and reach 

 the liver, where they undergo an asexual prolifera- 

 tion within liver cells. From these the young 

 merozoites are liberated and reach the general cir- 

 culation, again as vermicules. It is the last stage 

 which is taken up afresh by the mites. Although 

 the sporocysts may occur in the salivary glands of 

 the mite as well as in other parts of the body, Mil- 

 ler found no reason to believe that the parasite is 

 inoculated into the rat by the bite of the mite. 

 The latter feeds only at night, leaving the host 

 in the day, and at a subsequent feed may well 

 reach a healthy rat, which in turn becomes in- 

 fected by eating a sufficient number of the mites. 

 Miller reproduced the infection also by this "nat- 

 ural" method. Other modes of infection, artificial 

 in character, proved to be unsuccessful. 



That insects may have a relation to the main- insects and 

 tenance and extension of some diseases caused by 

 multicellular parasites is illustrated by the trop- 

 ical and subtropical disease of filariasis, of which 

 elephantiasis is one of the most pronounced clin- 

 ical symptoms. The larval worms often exist in 

 large numbers in the blood of man, particularly 

 at night. When certain mosquitoes suck infected 

 blood at this time one or more of the worms is 

 ingested, undergo further development, and eventu- 

 ally bcre through the stomach wall and reach the 

 breast muscles of the insect. The exact manner 

 in which the parasites are reinoculated into man 

 is unknown. It was supposed by Manson that 



