434 Some Relation? of Biology to Agriculture. 
sporidia, (4) Microsporidia. It should be clearly understood that 
these organisms are in no way related to the Bacteria. 
The Gregarinidia are best known in the form of minute worm-like 
parasites in the intestines of insects and otiier invertebrate animals. 
The Sarcosporidia (sarx, flesh) are so named from the circumstance 
that they are generally found in the muscular tissues of verte- 
brate animals. They have long been known in the flesh of pigs, 
sheep, and other animals, where they may occur in considerable 
numbers without appai'ently aff'ecting the health of their host. 
When present in large numbers, however, they may give rise to 
various symptoms, according to the group of muscles involved. 
They are, moreover, not confined to the muscular fibre, for they 
occur in the connective-tissue of the cesojihagus (or gullet) of the 
sheep, forming there tumours of considerable size. The third order 
is not of agricultural interest. The Microsporidia include organisms, 
the spores of which ai-e so small that they have been mistaken for 
Bacteria. They occur as parasites of the tissue- elements of insects, 
and, in the form of the pebrine of the silkworm, have led to enormous 
losses in silk culture in Europe. M. de Quatrefages calculated that, 
in the first thirteen years after the outbreak of pebrine, France lost 
40,000,000Z. from the ravages of this sporozoon. 
Of the Gregarinidia there is a group, the Coccidia, which are 
true cell-parasites, though a brief free, or wandering, stage in their 
career permits the young forms to invade new cells or new hosts. 
The best known is Coccidium oviforme, from the liver of the rabbit. 
It occurs in caseous nodules and cysts of the liver, which are full of 
the parasites in their encapsuled stage (the so-called psorosperms). 
Several cases are recorded in which man has been attacked by the 
same parasite, and in one instance twenty cysts full of coccidia were 
found in the liver. There seems to be little doubt that cysts of this 
nature, full of caseous material, have often been misinterpreted in 
the past, and closer attention in the future may establish that such 
psorospermosis of the liver is not so rare as has been supposed. The 
epidermal cells of the skin are also subject to attacks of Coccidia, 
and PfeiSer has given a detailed account of the forms which cause 
a contagious skin-disease in poultry, and which were originally 
described by Bollinger in 1873. The cells are invaded by the 
Coccidia, and their nuclei are thrust aside as the parasite grows and 
proceeds to sporulation. The spores are at once capable of pi'opa- 
gating the disease, which, therefore, may be artificially produced by 
inoculation — and, indeed, if planted on the mucous membrane of the 
throat, instead of on the skin, the spoi'cs take on a flagellate, instead 
of an ama'})()id, form, but penetrate the epithelial cells and give rise 
to a diphtheritic condition, which is very contagious anu)ngst the 
poultry exposed to infection. Molluscum contagiosujn and certain 
other forms of skin-disease in the human subject are likewise attri- 
buted to Coccidia, and it is piobable that these organisms will be 
proved to have a close relationship to the development of cancer. 
Scheurlein's bacillus t)f cancer has turned out on examination to 
have nothing to do with the disease. 
