


154 THE NORTHERN MICROSCOPIST. 

with scales, which patches are very variable in size. It is important 
to observe that a single small patch of this kind may be seen upon 
a fish otherwise perfectly healthy. The patch once formed rapidly 
increases, while the central portion undergoes an important change, 
and the underlying tissue can be lifted up in soft flakes from the 
derma, or true skin, which it covers. As the patch spreads, the 
true skin sloughs, and a sore is formed which may extend down to 
the bone, while it passes outwards into burrowing sinuses. This 
causes great irritation, and the fish dashes wildly about, thus, in 
all probability, aggravating the evil. One vast sore may cover the 
top of the head, from the snout to the nape, and even extend over 
the gill-covers. The disease also enters the mouth, and is said to 
attack the gills, though Prof. Huxley has not found it so in any 
fish which has come under his observation. ‘The fish which suc- 
cumb to the disease grow weak and sluggish, seeking the shallows 
near the banks of the river, where they finally die. A disease 
similar to that described has been known among salmon in North 
America and Siberia. The Saprolegnia, which is the true cause of 
the salmon disease, is closely allied to the Peronospora, the cause 
of the potato disease. 
It was already known that the papyraceous slough-like substance, 
which is seen to coat the skin of a diseased salmon, when subjected 
to microscopical examination, is composed of a number of fine 
filaments which are terminated by elongated oval enlargements or 
zoosporangia. Within these the protoplasm breaks up into 
numerous particles, each less than goyq of an inch in diameter. 
These particles or zoospores are set free through the opening 
formed at the apex of the zoosporangium, and become actively or 
passively dispersed through the surrounding water. 
Prof, Huxley could find no satisfactory information as to the 
manner in which the fungus enters the skin, the exact nature of 
the mischief which it does, or what ultimately becomes of it. He 
therefore made a careful examination both of the healthy and the 
diseased skin, properly hardened and cut into thin sections. 
He also tried experiments on the transplantation of the Sapro- 
legnia of living salmon to dead animal bodies. The body of a 
recently killed housefly was gently rubbed two or three times over 
the surface of a patch of the diseased skin of a salmon, and was 
then placed in a vessel of water. In the course of 48 hours 
innumerable white cottony filaments made their appearance. As 
these filaments had approximately the same length, the fly’s body 
became enclosed in a white spheroidal shroud, having a diameter 
of as much as half an inch. ‘These filaments in size, structure, 
and the manner in which they gave rise to zoosporangia and zoos- 
pores were precisely similar to the hyphe of the salmon fungus, 
and the characters of the one and of the other prove the fungus to 
