196 PARASITISM 



the corium and give rise to minute papilla-like protuberances, which 

 may run together, continually increasing by peripheral growth. Blan- 

 chard considers these parasites to be sporozoa, but doubts their affinity 

 with the coccidiidia (Liihe, Minchin). 



The genitalia are frequently the seat of infection for several kinds 

 of protozoan parasites; Trypanosoma equiperdum, Dofl., for example, 

 the cause of dourine in horses, is transmitted solely by coition, the 

 flagellates getting into the blood by penetrating the epithelium. Simi- 

 larly, with Trypanosoma gambiense, the cause of sleeping sickness in 

 man, the organisms are said to pass from person to person in this 

 way (Koch), while the organism of syphilis in man Treponema palli- 

 dum is readily transmitted from person to person by coition. Rest- 

 ing or encysted stages' of the latter organism are unknown, but vitality 

 is apparently retained for long periods, for infection may be brought 

 about by contact with places contaminated by infected persons; abra- 

 sions and chapped surfaces are particularly dangerous. 



(c) Transmission by Inheritance. The transmission of protozoan 

 parasites by inheritance is only a modified form of contact trans- 

 mission, and might well be expected in the case of such parasites as 

 are capable of independent motion. It is satisfactorily established 

 at the present time that bacteria are not transmitted from mother to 

 child and that bacterial infection in utero is practically nil. With 

 protozoa, on the other hand, infection in utero by way of the placenta 

 and umbilical cord is fullv established in some cases, while in the 



i 



lower animals, such as invertebrates and aplacentalia among verte- 

 brates, inheritance of such disease-causing forms is much more 

 common. 



Pasteur ('58) early discovered that the only successful means of 

 combating the silkworm disease, due to Glugea (Nosema) bombyces, 

 was to carefully examine the eggs of the insect for cysts and to destroy 

 all that were found to be infected. Careful prophylaxis of this kind, 

 together with proper scrutiny of food, finally put an end to the inheri- 

 tance of the disease from generation to generation and brought to a 

 close a long-continued epidemic which had cost nearly one thousand 

 millions of francs. The later observers have placed such inheritance 

 among insects and arachnids upon a much safer basis, and in many 

 cases the transmission of protozoa from parent to offspring is fully 

 established. Smith and Kilbourne ('91) discovered that ticks belong- 

 ing to the genus Rhipicephahis (Boophilus) draw blood from cattle 

 infected with Babesia bovis (Piroplasma bovis), and convey the infec- 

 tion in time to some new host. Koch observed that the ova of ticks 

 were actually infected, and that the young, in addition, feed upon the 

 infected blood, so that the second generation transmits the disease, 

 and Christophers ('07) showed that reproductive bodies of Babesia 

 (Piroplasma) canis penetrate the ova, either in the ovary or during the 



