366 General Notes, 
have not occasion to keep track of the literature concerning the 
minute organisms that cause disease. A few of the more general 
oints can be stated here. Contagious disease, wherever it has 
been traced to its origin, has proved to be the phenomenon of para- 
sitism. This address is limited to a discussion of epidemics 
caused by Fungus or Protozoan parasites. s 
Of the Protozoan diseases of insects, pebrin of the silkworm is the 
best known example. There has been much discussion regarding the 
position of this parasite; butthere can be no longer a reasonabledoubt 
of its animal nature, or of its agreement in general characters with 
those forms now commonly included under the head Sporozoa, a 
parasitic-subdivision of the Protozoa of which Gregarina is per- 
haps the best known type. The life history of this parasite is 
very simple, and may be thus briefly summariz 
he minute oval spores, colorless, highly refractile, homogeneous 
in appearance, 4 y long by 2 u wide, when swallowed with the 
food, penetrate in some way unexplained the cuticle of the alimen- 
tary canal, and, in the cells of the epithelium, open at one end an 
emit their contents, each in the form of an ameeboid speck of 
protoplasm. This grows to a spherical body, and, by a process of 
internal segmentation common to the Sporozoa, is soon conve 
into a mass of spores, each like the original. These spores every- 
where undergo a like development, and load all of the tissues with 
their products, slowly and gradually arresting all of the functions 
of life. Their vitality is temporary — Pasteur’s experiments 
showing that they will not germinate five weeks after drying out 
— and the disease is consequently maintained only by virtue of its 
hereditary character. 
Other forms of Microsporidia have been found in at least ten 
species of insects enumerated by Forbes. : 
Although pebrine, and presumably other diseases of this nature, 
can be conveyed to healthy insects by treating their food with the 
dejections of affected individuals, the economic application of these 
diseases is limited to artificial measures for developing and acceler- 
ating them wherever they may be found, and to the transfer of 
them from one species to another. For there is not the slightest 
probability that the Sporozoa can be artificially cultivated outside 
of the bodies of the animals that they infest. 
The notable fungous diseases of insects are readily divisable 
into two principal groups: Schizomycoses, produced by Bacteria, 
and Hyphomycoses, due to Fungi that form a more or less evident 
mycelium of cylindrical threads (Hyphomycetes and Pyrenomycetes). 
These are roughly distinguishable in two important particulars: 
(1) The bacteria invade the body from within, by way of the 
alimentary canal; and the thread fungi penetrate from without 
through the skin or spiracles ; (2) Death from a schizomycosis 18 
followed by rapid decay, which soon reduces the tissues to a putr 
