No. 490] NOTES AND LITERATURE 



!!>«) 



infected. It has long been known that young produced by in- 

 fected licks will tnuisniit certain diseases even though they have 

 never come in contact individually with cases of the disease. 

 The demonstration in the ova of such forms as discovered by 

 Koch furnishes evidence of the manner of this transmission. 

 Christophers lias followed carefully the formation of these 

 bodies and their penetration into the ova, where they become 

 spherical resting stages. He has also traced these bodies through 

 larva to nymph and thinks that when the latter become adult 

 the parasites have migrated into the salivary glands. It has 

 long been known that Texas fever was conveyed by the progeny 

 of infected ticks, but the demonstration of the infective agents 

 has heretofore eluded observation. 



Several authors, among whom Carter 7 may be mentioned, have 

 shown that Spiroc/un fa Duttoni infects the ova of ticks which 

 suck the blood of hosts harboring this parasite, that the organisms 

 multiply in the ova and that by them the new generation of ticks 

 is infected and may transmit the disea.se produced by the para- 

 site. Other instances of the same type might be added to the 

 list. The process may. however, go one step farther. 



Recently reported investigations of several observers show that 

 in the housefly a parasitic flagellate infects the ova and thus the 

 subsequent generation of its host. Since the host is no longer a 

 blood-sucking insect, there is no possibility of a sanguinicolous 

 generation of the parasite in some other host. Probably the 

 hereditary method is the only one by which the parasite is 

 propagated and new generations of flies are infected, although 

 it is possible that encysted forms, discharged in the feces, might 

 be taken up in the food of some other fly. It is interesting to 

 note in this connection some work done in my laboratory by Mr. 

 L. D. Swingle, who has followed out the life-history of a similar 

 flagellate parasitic in the sheep-tick. As is well known, this host 

 is really a degenerate fly, and this parasite has, so far as can be 

 ascertained, no relation to the blood-suckinu' habit of its host. 

 It infects the ova and in a resting stage awaits there the devel- 

 opment of the next generation, but no stages were found indi- 

 cating any other method of transmission. 



These instances just outlined differ radically from those noted 



