SPOROZOON PARASITES OF FISHES. 195 



used without a cover glass and reveals most of the details necessary to recognize the 

 presence of Protozoa or other unusual histological conditions. A mechanical stage is 

 indispensable. 



Three organisms are involved in most of the Futiduhis ulcers, rarely a fourth. A 

 thick, short bacillus is the most abundant. A long, slender bacillus is less common. 

 The Sporozoa are represented by a species of Myxoholus, and in one case a species of 

 Chloromyxum. From the evidence in the following account it will be learned that the 

 primary attack upon healthy tissues, in a certain proportion of the diseased fish, is prob- 

 ably made by the long bacillus. At least a few and probably many of the diseased fish 

 are primarily attacked by Myxosporidia. The short bacillus is more or less incapable 

 of rapid growth in living cells of any kind. While it is not within our province to make 

 an exhaustive study of the fungus diseases, it has been necessary to ascertain to what 

 extent they participate in bringing about these pathological conditions. 



EXPERIMENTS TO DETERMINE CHARACTER OF INFECTION. 



The following experiments were carried out in order to gain some accurate infor- 

 mation as to the conditions whereby healthy fish are infected and the possibilities of 

 their recovery. At the time it was not possible to discriminate between fish that were 

 infected by a fungus and those that were infected by a sporozoon. It will be apparent 

 that the experiments are not vitally affected by the kind of parasite present. 



Forty fish were divided equally and placed in two 5 -gallon aquaria. These fish 

 had been seined in the usual manner and brought to the laboratory on board the steamer 

 Phalarope in large milk cans. The trip from the collecting grounds (Menemsha Bight) 

 usually requires about one and (?ne-half hours. The cans accommodate from 200 to 

 300 fish each. A hose supplies them with fresh water. The 40 fish used in this case 

 were examined carefully and found to be free from all visible integumentary disturbance. 



First stage. — Aquarium no. i was carefully cleaned and sterilized. Aquarium no. 2 

 had contained diseased fish, and 2 diseased fish were allowed to remain with the 20 

 fish used in the experiment. Contaminated fish from other sources were always kept 

 in this jar. Both groups were fed about every 48 hours. After a period of 1 1 days 

 none of the fish in the clean jar showed any signs of disease. From this fact we con- 

 cluded that they were free from the disease and suitable for experimentation of a dif- 

 ferent kind. After the same period (11 days) the contaminated jar had one fish with a 

 conspicuous sore. It died a day later. 



Second stage. — On the eleventh day one of the fish in each of the two jars was 

 operated upon. A scale or two was removed and the integument pierced with a scalpel 

 just back of and dorsal to the opercle. More diseased fish were introduced into aquarium 

 no. 2. Five days later the fish in aquarium no. i which had been operated upon died. 

 The integument, at the point where the incision had been made, had developed a typical 

 sore. At this time the fish with the pierced integument in no. 2, being a large fish, had 

 not developed a sore of noticeable extent. 



Third stage. — On the sixteenth day of the experiment, all fish having recovered in 

 both no. I and no. 2, scales were removed and the integument of all the fish was pierced 

 in the same manner as was done with the two above mentioned. Two days later almost 

 all of those in jar no. 2 had developed marked diseased patches at the very spot where 

 the integument had been pierced. No noticeable change had taken place in the fish of 

 the clean jar. Four days later one fish in jar no. i died from the effects of the rapidly 



