SPOROZOON PARASITES OF FISHES. 20I 



common when the short bacillus occurs abundantly; nor are there any of the short 

 bacilli. The normal striated fibers possess few if any of the germs and they seem to be 

 numerous in proportion as the sarcoplasm is degenerate. These are not the conditions 

 we would expect of a virulent parasite unless its primary attack is through the agency 

 of a toxin. There is a second factor to be considered, however, inasmuch as numerous 

 myxoplasms and autospores of M. musculi occur in some of the less decomposed por- 

 tions of the same tissue. With the evidence at hand bearing upon the virulence of the 

 two bacilli, the most natural conclusion is that the short bacillus is a saprophyte, that 

 the long bacillus is either a facultative parasite upon the post tissues, which has been 

 reduced in vigor by the Sporozoa already established therein, or perhaps a true parasite, 

 in which case there are frequent double infections, the long bacillus and Myxosporidia 

 together preparing the way for the saprophytic short bacillus. 



The long and short bacilli are easily distinguishable by their size, shape, and habits. 

 The long bacillus is 0.7/t in diameter and usually at least 2.5,« long, but it may be 22/£ 

 long, without any noticeable increase in diameter. (Fig. ii,pl. xx.) They have tapered 

 ends, especially those which have but recently divided. Sometimes the long type 

 divides, forming short rods, but they are then in chains. They never occur in clusters 

 as in figure 10, plate xx. The short type is never coiled, never so long, and always thicker 

 than the long bacillus. They are b'oth encountered in smears which include the fluids 

 of completely broken-down tissues, but the short form is always abundant in such 

 fluids, while the former is rare. One is frequently clustered and in regular pockets, the 

 other isolated or scattered and, if in cavities at all, they are irregular crevices. 



SPOROZOA ASSOCIATED WITH ATROPHIED TISSUES. 



From the evidence in the foregoing pages and borne out by that which is to follow, 

 it is certain that a sporozoon causes the primary degeneration of muscle, gill, and pos- 

 sibly integumentary tissues, resulting in pathological conditions which are quite as 

 characteristic as when the bacillus is the primary parasite. In one tissue which was 

 sectioned (fig. 18, pi. xxi) the degeneration of the muscle fibers is identical to that where 

 bacteria alone have been obser\'ed (p. 200) . The atrophied fibers, which contain numerous 

 scattered Sporozoa (p. 198, 203), occur in groups of twoor three here and there through- 

 out the fragment of flesh. Frequently, in both sections and smears, degenerate muscle 

 fibers occur in which there are cells similar to the above but with neither nucleus nor 

 cytoplasm stained ; also large amoeboid masses of granular cytoplasm without any visible 

 nucleus (fig. 13, pi. xx). Usually such foreign cells occur in tissues when either myxo- 

 spores or multipficative stages are more or less abundant. 



In one or the other of the above stages the sporozoon has been positively identified 

 with the disease in 18 of the 85 fish which have been examined. On the other hand, 

 many degenerating fibers have been encountered both in smears and sections in which 

 neither Protozoa nor bacteria could be found. In such cases there is about equal 

 lack of evidence that either of the above are the causal agents of such disintegration. 

 While it is probable that the majority of the sores are caused by the inoculation of a 

 wound by a germ, there is less evidence of a primary attack upon the tissues by the 

 bacteria, except through a widespread toxin, than by Sporozoa. In this connection there 

 is probably a significant difference in the external appearance of diseased tissues which 

 are primarily due to the sporozoon attack and those which are caused by bacteria. 



