656 A MANUAL OF BACTERIOLOGY 



nuclear leucocytes. It is encapsuled and contains a single granular 

 nucleus. Encystment with sporulation occurs in the bone- 

 marrow, and a sexual development is stated to occur in a tick. 



Another typical form, Hcemogregarina (Drepanidium, Lan- 

 kesterella) ranarum inhabits frogs (Eana esculenta), and possesses 

 both an intra- and an extra-corpuscular phase. In the former the 

 parasite occurs as an elongated gregarine-like body within the 

 red corpuscles. The extra -corpuscular phase, commencing within 

 the corpuscles, ends in an elongated organism possessing a ver- 

 micular movement, and free in the plasma. Similar parasites are 

 frequent in the lower vertebrates, e.g. snakes. 



Order, Myxosporidia 



In this group the trophozoite is amoeboid, and the species are 

 almost exclusively parasites of fish, in the young stage being 

 intracellular (" fish psorosperms "). 



Order, Microsporidia 



The Microsporidia are cell parasites of invertebrates, especially 

 arthropods, and the trophozoite is more or less amoeboid. 



Nosema bombycis causes pebrine, a disease of silkworms, which 

 is of considerable importance commercially, for the silk industry 

 in France was once threatened with extinction owing to its ravages. 

 The infected worms do not grow normally, cease to eat, and die, 

 or may form abnormal pupae. Within the body of the affected 

 worms a large number of roundish, highly refractile corpuscles are 

 found. Pasteur ascertained that the disease was propagated 

 by healthy worms eating with their food the excreta of infected 

 ones. The moths were thus affected, and laid infected eggs. By 

 allowing each moth to lay its eggs separately, and subsequently 

 examining the body of the moth microscopically, he was able 

 to separate the healthy from the diseased, and the eggs of the 

 former were kept, while those of the latter were destroyed. 



Another disease of silkworms is known as flacherie, but is due 

 to a bacterium, Micrococcus bombycis. It is contagious, and 

 can be transmitted by inoculation. 



The Isle of Wight bee disease was supposed to be caused by a 

 parasite (Nosema apis, Fantham) belonging to this order. Rennie 

 now states that it is due to a minute mite which blocks the 



