SPOROZOON PARASITES OF FISHES. 197 



PATHOLOGICAL CONDITION OF THE TISSUES. 



Those typical sores in which Sporozoa can not be positively demonstrated, and of 

 which a part may be due to bacteria, present the following histological conditions. They 

 are probably primarily exogenous ulcers in which there is at times abundant granular 

 degeneration derived both from lymphocytes and haemocytes. Sometimes at the nidus 

 of the necrotic area there are small cysts or abcesses containing small lymphocytes. 

 Usually the vascular tissues abound and erythrocytes preponderate. There is a decided 

 tendency at times for the epidermis to form a cicatrix. Again it gives evidence of 

 sloughing off. But so far as the muscle tissue is concerned universal necrosis is common. 



The involved epidermis contains numerous nonstaining globules or masses of 

 variable size (fig. 36, pi. xxi), as to the exact nature of which we are yet in doubt. They 

 are also to be found in the connective tissue of the dermis and in certain partly atrophied 

 muscle fibers when adjacent to degenerate tissue. They seem to be more numerous in 

 the epidermal cells wherein there are obvious signs of disintegration (pp. 198, 201,203). 

 Inasmuch as there is a nonstaining zoogloea or secretion about some of the bacilli that are 

 commonly found in these parts, which frequently prevents them from staining (see p. 

 200), it is possible that these bodies are of the same nature and contain one or more of the 

 bacilli. No doubt many are fat globules, but some are certainly not. Some of these 

 bodies in sections of muscle containing myxoplasms possess a well-defined nucleus. 

 (Fig. 12, pi. XX.) 



In smears of integument, it is occasionally possible to find fragments of considerable 

 size having the epidermal cells more or less filled with the short bacillus referred to above. 

 It is not difficult to prove, by the observation of fresh material or by comparison of tis- 

 sues of different stages of degeneration, that the short bacillus is seldom found in normal 

 living cells. It is therefore not probable that the primary attack upon the epidermis is 

 caused by this particular organism. The long slender bacillus is less commonly en- 

 countered in the dermis and epidermis. There is but little evidence in support of the 

 view that it is the initial cause of epidermal decadence. 



The muscle fibers beneath these infected areas present an interesting condition. To 

 the naked eye there seem to be numerous white threads running parallel with the muscle 

 cells. This is especially true of well-advanced ulcers. When seen under the microscope, 

 such flesh has but few normal fibers with fibrillae and cross striae. Most of them have the 

 sarcolemma and interfibrillar connective tissue still sufficiently intact to retain the general 

 external structure of the separate fibers, but the myoplasm is in various stages of de- 

 generation. We conclude, therefore, that the parasite is intracellular and does not pass 

 readily from one fiber to another. The muscle fibers sometimes undergo degeneration 

 more or less uniformly throughout their length. In some cases it is more rapid in the 

 immediate vicinity of the parasites. This we know from sections where the fibrillae show 

 in places adjacent to degenerate myoplasm in which Sporozoa are numerous. One side 

 or the middle may be far more degenerate than the rest of the fiber. The parasites have 

 probably passed through these regions. The first indication of change is the loss of 

 fibrillation. It is rather difficult to find a parasitized fiber showing normal fibrillation 

 (fig. 13, pi. XX). The pale bands of muscle fibers next become granular (figs, i and 2, 

 pi. xx) and at length the sarcous elements break up into large pieces. Eventually there 

 is total granular atrophy of the fiber within the sarcolemma. In certain cases, usually 



