24 PEACTICAL PARASITOLOGY 



natural conditions, this occurs as a result of the chemical action of the 

 intestinal secretion of the caterpillar, and immediately afterwards the 

 naked amoeboid germ emerges from the cnidospore and buries itself 

 in the epithelial cells of the intestinal canal. The parasite now 

 multiplies rapidly by repeated binary fission. The process of separa- 

 tion, however, is frequently incomplete, and the daughter-individuals 

 thus form themselves into long chains resembling a rosary, at right 

 angles to the free surface of the affected epithelial celL The infection 

 spreads with great rapidity from the intestine to all the other organs 

 of the host, and, eight days after the ingestion of infected material, the 

 entire body of the caterpillar swarms with parasites. Wherever, as 

 the result of this rapid increase, there is an insufficiency of nutriment 

 or of space, the individual parasites form cysts and become converted 

 into cnidospores. These may be found in the intestinal tract as early 

 as three days after infection. Not only is infection conveyed directly, 

 by means of faeces containing parasites, but it may be congenital, the 

 eggs of the mother having become tainted. The organism is trans- 

 missible to other varieties of caterpillar, as, for instance, Arctia caja. 1 

 Many caterpillars, both exotic and native, support parasites apparently 

 similar to Nosema bombycis, but of which little is known. If affected 

 caterpillars are obtainable, cover-glass preparations and, more im- 

 portant still, thin sections should be made from them. The latter 

 should not exceed 2 /JL in thickness and should be prepared from organs, 

 preferably the intestine. They should be fixed in alcoholic solution 

 of mercuric chloride. 



The common cockroach, Periplaneta orientalis, harbours a parasite 

 which is well worth studying. It is a Microsporide known as Pleisto- 

 phora periplaneta (Lutz and Splendore), 2 and is found in the Mal- 

 pighian vessels of its host. The intestine should be removed in the 

 manner already described, and the long, fine Malpighian vessels, which 

 enter the intestine at the junction of the middle with the terminal 

 portion of the intestinal tract, should be carefully separated and freed 

 from fat. For examination they should be cut in small pieces and 

 put into saline solution. The parasites show amoeboid movement ; 

 their diameter varies from 0'002 to O055 mm., and the number 

 of their nuclei from one to sixty or more. Where infection is very 

 severe the cells of the Malpighian vessels become pathologically 

 changed (less granulated than the normal), although the parasites 



1 Stempell, " Die Pebrine-Krankheit der Seidenraupe," Sitzber. d. med. naturwiss, 

 Gesellsch. Miinster i. W., 1907. Meeting of June 25, 1907. 



2 W. S. Perrin, " Observations on the Structure and Life-history of Pleisto- 

 phora periplanetce, Lutz and Splendore," Quarterly Journal of Microscopical 

 Science, vol. xlix, 1906, pp. 615-633. 



