MICBOSPORIDIA 23 



of the vesicle (fig. 3). This thread is shot out with great velocity, 

 either spontaneously or under the influence of certain stimuli. Of the 

 several nuclei of the cnidospore, a certain number (generally two) go 

 to the formation of the soft bodies (amosboid substance of sporoplasm) 

 which escape when the shell opens ; others (cnidoblast nuclei) play a 

 role in the formation of the nematocysts ; while others again (shell 

 nuclei) form the shells. On account of their possession of the 

 characteristic nematocyst or " cnidoblast," the Microsporides, Myxo- 

 porides and Actinomyxides are usually classed together under the 

 name of Cnidosporides. The Sarcosporides are usually included in 

 this group, in spite of the fact that they possess neither shell nor 

 cnidoblast and have one nucleus only. 



Many different methods of inducing the cnidospore to discharge 

 the nematocyst have been recommended, but of these none is invariably 

 successful. The best method is to examine the organism in the fresh 

 gastric or intestinal secretion of its host. In some cases, the addition 

 of iodine (solution, tincture, or iodine in iodide of potassium) is 

 attended by good results ; while with other species distilled water, 

 boiling water, potassium solution, ammonia, strong mineral acids (nitric, 

 sulphuric), ether, and other chemical reagents will achieve the desired 

 effect. In a few cases, mechanical pressure is a sufficient stimulus, 

 Practical experiment is, however, the only means of determining 

 which of these measures will react upon the particular species under 

 observation. 



Order 1. Microsporidia. 



The Microsporides are recognized by the peculiar structure of their 

 cnidospores, which are extremely small, either pear-shaped, oval, 

 or oblong in form, and appear always to contain four nuclei. They 

 are furnished with never more than one large nematocyst, which, 

 as a general rule, can be seen only after treatment with reagents. 

 The Microsporides are very numerous and are found in the Arthropods 

 (crustaceans, arachnoids, insects), in fish and in the tortoises. They 

 are said to occur in man, but the assertion lacks proof. Certain 

 species inhabit the hollow organs of their host, others are cell or 

 tissue parasites. 



From a practical point of view, the most important of the Micro- 

 sporides is undoubtedly Nosema bombycis, Naeg., the originator of 

 the "Pebrine " of silkworms. It is peculiarly deadly to the silkworm, 

 and penetrates into every organ of its host. Its small size, however, 

 renders it extremely difficult of detection. When treated with con- 

 centrated nitric acid the entire organism swells and the nematocyst 

 becomes visible ; some varieties will even project their thread. Under 



