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MORPHOLOGY 375 



forms, consisting mainly of spherical or club-shaped swellings on the ends of the 

 filaments. 



If, instead of making film preparations, the growth of the organisms is followed 

 by 0rskov's (1923) agar-block technique, it will be seen that in some species the 

 aerial mycelium gives rise, without preliminary segmentation, to circular or oval 

 " spores." There is evidence that these " spores " are rather more resistant to 

 inimical agencies generally than the plain mycelium. They may, for example, 

 resist moist heat at 65° C. for as long as 3 hours. The segmented mycelium, 

 observed in many species, is no more resistant, however, than the unicellular 

 mycelium. 



All members are non-motile and all, with a few possible exceptions, are Gram- 

 positive. The anaerobic types are uniformly non-acid-fast. The aerobic types 

 may be differentiated into : 

 (1) acid- fast ; these resist 

 decolorization with 1 per 

 cent, sulphuric acid for 5 "^^"^^ 



minutes, but are usually ^\^ '"^^T^^N 



decolorized by the appli- >_ \ 



cation of 25 per cent. \ 



H2SO4 for a similar length 

 of time ; there is, however, 

 a marked variation in the 



acid-fastness of different ^^ ^< 



species. (2) Non-acid-fast. 



In the animal body 

 the morphology is often 

 different from that on cul- — -^ /-, _ • 



ture media. The anaer- N / 



obic Wolff-Israel type \-^=*^ ^^d^ '^ 



grows in the form of A^ 



definite colonies, which 

 appear in the pus or in 



sections of the tissues as Fig. 59. — Aclinomycts graminis X 1000. 



granules or " Drusen." From a broth culture, 24 hours, 37° C. aerobically. 



When crushed and ex- 

 amined microscopically these granules are seen to consist of a central fila- 

 mentous Gram-positive mycelium surrounded by a peripheral zone of large, 

 Gram-negative clubs. In old colonies the mycelium is replaced by a mass of 

 short Gram-positive rods and coccoid bodies, which appear to have resulted from 

 the disintegration of the filaments. The clubs vary in size, but may be as long 

 as 10 ju and as broad as 5 jli. Their mode of origin has given rise to much dis- 

 cussion. On the whole it seems probable that there are two entirely different 

 types of club, one observed in artificial culture and derived from the organism 

 itself, the other observed in the animal body and derived from the host. The first 

 type, or " culture club " as 0rskov (1923) calls it, represents the swollen end of 

 the mycelial filament. The second type or " tissue club," as we may call it, 

 appears to be due to the deposition around the end of the filament of some 

 material, probably rich in lipoid, by the tissues of the host. Tissue clubs are 

 observed, not only in ray-fungus infections, but also in lesions caused by other 



