8 BULLETIN 780, U. S. DEPARTMENT OF AGRICULTURE. 



ber 16. On the twenty-ninth of the same month all of the bees 

 examined from the colony were found to be infected. The results 

 of these experiments strongly indicated that the disorder in which 

 the oval bodies were found was an infectious one and that the bodies 

 were parasites which bore a causal relation to the disease. Other 

 studies made by Donhoff (1857, September) indicated that the 

 parasite was quite prevalent in Germany but that there were colonies 

 apparently free from infection. 



About 50 years later Zander (1909) inoculated colonies experimen- 

 tally by feeding material containing the oval bodies he had encoun- 

 tered in his studies. In bees from the colonies inoculated he demon- 

 strated that the oval bodies were in the walls of the stomach. This 

 fact showed still more conclusively that there was an infectious 

 disease of adult bees in which the oval bodies were parasites bearing 

 a causal relationship to the disease. 



The oval bodies studied by Zander and those studied by Donhoff 

 in all probability are the same. To Zander, however, is due the 

 credit for 'having determined their true nature. Together with 

 Doflein he (1909) classified the germ as a protozoan (a one-celled 

 animal parasite) belonging to the group Microsporidia and to the 

 genus Nosema. Zander gave the name Nosema apis to the species 

 ' he found in the honeybee. 



The parasite Nosema ajns grows and multiplies for the most part 

 in the epithelium of the stomach (fig. 3 ; Pis. II and III) of the adult 

 bee. Occasionally, but rarely, it is found within the epithehal cells 

 of the Malpighian tubules (Pis. II and III). When Nosema apis is 

 encountered in making an examination for the parasite it is the spore 

 form (fig. 4 ; PL III, G, H) that is most often encountered and most 

 readily recognized. Viewed microscopically the spore in unstained 

 preparations is seen to be a small, refractile, more or less oval body 

 varying somewhat in size but measuring about 2/10,000 of an inch 

 in length and about 1/10,000 of an inch in width. Its width seems, 

 however, to be slightly greater than one-half its length.^ The spore 

 is surrounded by a somewhat resistant coat which tends to maintain 

 for it a constant form. It is not, however, a rigid structure, since, 

 when studied in fresh preparations, it will be seen to bend to and fro 

 as it is carried along by a current under the cover glass. 



The manner in which a bee becomes infected with Nosema apis is 

 in general as follows : Spores which have left the body of an infected 

 bee with the excrement are ingested by the healthy adult bee. The 

 environment within the stomach of the bee is favorable for the 



1 Measurements were made of spores in smears stained with iron hematoxylin and of others in prepara- 

 tions made by an India-ink method. In making the latter preparations thin smears of the spore containing 

 material were made and allowed to dry, and over these smears a thin film of midiluted India ink was spread. 

 The average length of the spores measm'ed in the stained preparations was 4.15 m and the averagefbreadth 

 2.06 fi; the average length in the India ink preparations was 4.46 it and the average breadth 2.44 m. 



