338 . PARASITIC DISEASES. 



favours the spread of pentastomum denticulatum, cysticercus 

 tenuicollis, and echinococcus, from the development within 

 the nasal sinuses of pentastomum tsenioides, and in its in- 

 testine of tgenia marginata and T. echinococcus. Also the 

 muscle trichinae of men may in some cases, especially when 

 they are few in number, be communicated: from dog to 

 man/' 



Of the internal parasities, or entozoa, affecting the domes- 

 tic quadrupeds, there are many, and have been classed under 

 two general heads infusoria and worms. 



The infusoria are constantly found in the bodies of ani- 

 mals. Sometimes they engender disease, arid no more in- 

 teresting illustration of this can be adduced, than that of the 

 Bacteria, belonging to the family of Vibrios, and which 

 have usually been described as rigid, filiform animalcules, 

 moving in a vacillating, rather than in a serpentine, or 

 undulating manner. These parasites vary from 2 to 5 

 millimeters in length. Bacteria were supposed to develope, 

 and live principally in putrid liquids, but M. Davaine has 

 found them in the blood of animals affected with splenic 

 apoplexy, and has observed, that putrefaction destroys the 

 infusoria as well as the blood. They can be transferred 

 from one animal to another by inoculation, and multiply 

 with very great rapidity in the vessels of their new host. 



The Bacteria kill the animals they invade, and if the 

 blood containing them is rapidly dried, the infusoria are 

 thereby preserved, and can resist the temperature of boiling 

 water. This explains how in some arthracic diseases, the 

 flesh of animals may prove deleterious after being cooked. 



Of the family of Monads, it is asserted, on the authority 

 of Leuwenhoeck, that Cercomonas urinarius is frequently met 

 with in horses' urine when fresh. 



In the stomach and intestine of the herbivorous quadrupeds, 



