THE ACTINOMYCETES, Vol. I 



tain specialized media, such as those con- 

 taining a high concentration of serum. 



Various reports concerning filterable forms 

 of actinomycetes are found in the literature. 

 It is sufficient to cite a recent contribution 

 by ]\Ional. Cultures of A. bovis were filtered 

 through a collodion membrane. When the 

 filtrate was supplemented with various nu- 

 trients, growth took place. This consisted of 

 filamentous forms and typical arthrospores ; 

 there were also a "symplastic stage," diph- 

 theroid forms, streptococcal forms, and a type 

 of cell similar to a T or a double Y. Suspen- 

 sions of .4. hovis obtained from culture col- 

 lections or isolated from human cases were 

 placed in collodion sacs, which were intro- 

 duced into the peritoneum of rabbits. After 

 the first and second passage, the animals 

 showed no symptoms of actinomycosis. 

 After the third passage, consisting in the 

 inoculation of the rabbit with the product 

 of the second passage, atypical actinomy- 

 cosis was produced, in which the parasite 

 was in the form of a symplastic or of a 

 diphtheroid bacillus. After the fourth pas- 

 sage, typical actinomycosis was obtained. 

 The conclusion w^as reached that cultures of 

 A. hovis contain growth elements that will 

 pass through a collodion ultrafilter. Erikson 

 (1940) did not confirm the ability of actino- 

 myces to give rise to filterable forms. 



Erikson emphasized the difficulties en- 

 countered in isolating an actinomyces from 

 the mixed flora obtaining in most patho- 

 logical material; the low fertility rate of 

 dismembered mycelial fragments and in- 

 dividual cells; and the need for anaerobic 

 methods of cultivation. Successful isolation 

 depends to a high degree on fresh material 

 containing a quantity of viable elements. 

 Although lOrikson stated that her experi- 

 ments "have disposed of the existence of a 

 filterable stage and have yielded no evidence 

 in favor of any hypothetical life cycle in- 

 volving either anacrolnc or aerobic forms," 

 Kriss ct al. (1945) stated that the hyphae of 



actinomycetes in a single colony may be so 

 thin as to lie beyond the limits of the visible 

 light microscope and may thus yield filter- 

 able forms. More recent studies on the sporu- 

 lation process of ^4 dmom//ces have been made 

 by Bisset, as shown later (Vol. II, Chapter 

 24). 



Nocardia 



According to Jensen, nocardias are char- 

 acterized by the early formation (when iso- 

 lated cells are allowed to develop into micro- 

 colonies) of an initial mycelium that sooner 

 or later divides into irregular rod-shaped 

 cells resembling mycobacteria or coryne- 

 bacteria and often becoming so short as to 

 look like cocci. The initial mycelium varies 

 in extent from hardly visible, irregular, 

 elongated rods with a few short lateral 

 branches, to something approaching that of 

 Streptomyces, from which it differs only by a 

 more loose and crumbly consistency when 

 the hyphae begin to divide. Swollen cells 

 that on fresh medium germinate with one or 

 more slender "germ-tubes" are of common 

 occurrence. The aerial mycelium of Nocardia 

 varies to a similar extent. It is often invisible 

 to the naked eye, and may be altogether 

 absent or may consist of a few short fila- 

 ments, which sometimes look like mere gran- 

 ules. At the other extreme, the aerial my- 

 celium may be abundant but composed of 

 elements resembling those of the vegetative 

 mycelium, usually less branched than in 

 Streptomyces, and usually not differentiated 

 into conidia-like spores. 



The nocardias are related, on the one 

 hand, to the mycobacteria, and on the other, 

 to streptomyces. This gradual transition 

 from one group of microbes to another must, 

 in the words of Erikson (1945), "be accepted 

 as another of the innumerable instances in 

 which nature prodigally overlaps manmade 

 taxonomic boundaries." In the early stages 

 of de^'elopment, nocardias are characterized 

 by the formation of an undivided substrate 



