1 6 REPORT ON THE DISEASES OF SILKWORMS IN INDIA 



The spore is a very minute oval body measuring as a rule 3-4/a * 

 in length and T5-2/A in breadth. Much larger spores than this are 

 occasionally got, some having been measured as much as from 6 to 

 10/a long. When seen in the fresh state, that is untreated by 

 reagents, little or no internal structure is visible. It appears as a 

 very bright oval body standing out as a rule clearly from its 

 surroundings. (Plate VIII, fig. 5.) It is this appearance, due to its 

 high refractive index, that makes it possible for the" spores to be 

 recognized under comparatively low powers of the microscope. 

 The " line " which is described (See Mukerji, 1899) is of course 

 merely an optical effect. When treated in a suitable fashion, 

 however, and coloured by certain stains^ the contents of the spore 

 are revealed. The internal structure of the spore varies somewhat 

 according to its stage of development, but taking a nearly fully 

 developed individual it presents an appearance such as is shown 

 in the Text-figure A, 1. The spore wall is seen to be thick. At each 

 end is a clear space or vacuole, and in the middle is a coloured por- 

 tion surrounding the inside of the spore like a girdle. This of course 

 refers to a killed and stained specimen : in the fresh spore this girdle 

 is colourless. This is the part that in a living spore would be 

 destined to infect a fresh caterpillar. Contained in this stained 

 portion are two darker, roughly circular particles, the nuclei : other 

 nuclei may at certain stages be seen, but as these have no very 

 evident connection with the future history of the organism, they may 

 be neglected. Very occasionally a faint, pear-shaped sac may be 

 made out towards the middle line and one end of the spore. But 

 this, is at best but a fleeting impression. If, however, the fresh spore 

 is treated by certain liquids, a very long thread is shot out from this 

 sac-like body (Text-fig. A, 2j and Plate III, fig. 4). The easiest 

 way to demonstrate this is to treat some fresh spores with hydrogen 

 peroxide when a vigorous shooting out of these polar filaments, as 

 they are called, will be seen (See Kudo, 1918). The use of these 

 filaments seems to be this : when spores of Nosema hombycis are eaten 

 by a silkworm, or if one directly feeds a caterpillar on spores for 

 experimental purposes, the juices in the gut act upon the spores and 

 if they are ripe, or fully formed, in a very short time after they 

 arrive in the gut the polar filaments are shot out, and seem to anchor 

 the spore to the gut wall. It is supposed that the digestive juice 

 of the caterpillar acts on the spore in the way that hydrogen peroxide 

 does and stimulates it to shoot out the filament. The peculiar thing, 

 however, is that if one treats spores with the digestive juice of a 

 silkworm outside the caterpillar's gut, say, on a microscope slide, 



* The " u " used in microscopic measurements is employed here on account of the con- 

 venience in writing it. It is one- thousandth part of a millimeter or roughly one -twenty. fire 

 thousandth part of an inch. 



