184 THE ANIMAL PARASITES OF MAN 



juice, when the spore reaches a new host, and serves to anchor the spore to the 

 tissue with which it is in contact, and thus allow of the emergence of the amcebula 

 in a situation suitable for its development. The polar capsule with its contained 

 polar filament has been compared with the stinging cells or nematocysts of the 

 Ccelentera, but it has a totally different function. 



The spores fulfil the purpose of effecting transmission to other hosts. In- 

 fection occurs by the ingestion of the parasites per os after their escape by some 

 means from their host. Thelohan and others have demonstrated that the valves of 

 the spores soon open under the influence of the digestive juices, thus allowing the 

 young myxosporidia to escape. Their further history is unknown ; but it may be 

 surmised that they either travel direct to the organs usually affected (gall bladder, 

 urinary bladder), or are distributed in the body by means of the circulatory or 

 lymphatic systems. 



The Myxosporidia that invade tissues are often deadly to their hosts. They may 

 be present in a state of " diffuse infiltration " when practically every organ of the 

 body may be infected, as in barbel disease (due to Myxobolus pfeifferi). On the 

 other hand, the parasites may be concentrated at one spot, when cysts, either large 

 or small, are produced. Such cysts occur on the gills of many fishes. A few addi- 

 tional important pathogenic forms are Myxobolus cyprini, the excitant of " pocken- 

 krankheit" of carp, and Lentospora cerebralis, parasitic in the skeleton of Salmonidae 

 and Gadidos. The skeletons of the tail, fins and skull particularly are seats of infec- 

 tion, and from the skull the Lentospora can spread to the semicircular canals, result- 

 ing in loss of power to maintain its balance on the part of the fish. On this account 

 the malady is termed " drehkrankheit." Young fish are more particularly infected. 

 Myxobolus neurobius infects the spinal cord and nerves of trout. 



Myxosporidia are divided into two sub-orders Disporea and Polysporea 

 according to whether they form only two or several spores during their growth. 

 The former include two genera limited to fishes, which are easily distinguishable by 

 the shape of the spores : Leptotheca, Thel., with a rounded spore, and Ceratomyxa, 

 The"!., with a very elongate spore. The larger number of genera belong to the 

 Polysporea, which are divided into three families : 



<i) Amoeboid germ with a vacuole f(a) With two polar capsules Myxidiidce. 

 the contents of which do not j 



stain with iodine. I (b) With four polar capsules. Chloromyxidcr. 



(2) Amoeboid germ with a vacuole stainable with iodine. Spores with two polar 

 capsules. Myxobolidce. 



For further subdivisions the differences in the spores are principally utilized. 



Order. Microsporidia. Balbiani. 



These are the organisms discovered in the stickleback by Gluge in 1834, and 

 in Coccus hesperidum by Leydig in 1853. They have since been found in numerous 

 other arthropods, especially insects. They acquired particular importance when it 

 was discovered that they were the cause of the "pebrine" disease ("gattina" of 

 the Italians) which caused so much destruction amongst silkworms (Bombyx mori). 

 Pasteur (1867-70) and especially Balbiani (1866) participated in the researches on 

 Nosema bombycis, and it was the latter who classed the "pebrine bodies" or " psoro- 

 spermia of the arthropoda" amongst the Sporozoa as Microsporidia (i882). ! The com- 

 plete life cycle of N. bombycis was described in 1909 by Stempell. The Microsporidia 

 are not confined to insects and arachnoids, they are now known to occur also in 

 Crustacea, worms, bryozoa, fishes, amphibians and reptiles. Certain tumours in 

 fishes, similar to those formed by many Myxosporidia, are produced by Micro- 

 sporidia. Fantham and Porter found that Nosema apis was pathogenic to bees 



1 C. R. Acad. Sfi. t Paris, xcv, p. 1168. 



