MORPHOLOGY. 



INVOLUTION FORMS. 



Under this name we designate swollen and distorted forms common in old 



cultures (fig. 21). Under what conditions do they 

 occur? Are they living or dead? Isolate in 

 hanging drops of bouillon and determine whether 

 the}- are stages in development or only degenera- 

 tion forms. Are Y-shaped or branched forms 

 such as occur in old cultures of B. tuberculosis 

 Koch, and in the root-tubercles of clover (fig. 22) 

 to be considered as involution forms ? Are such 

 organisms fungi or bacteria ? Branching forms 

 have been detected by man}- observers. (Consult 

 numerous citations in the Bibliography of General 

 Literature, X). The most recent paper is by Albert 

 Maassen (Arb. a. d. Kais. Gesundh., Bd. XXI, H. 3, 



Fig. 18.* 



1904, p. 377, 6 pi.). He found chloride of lithium specially 

 advantageous for provoking these growths, which are re- 

 garded as teratological. He obtained them in 24 hours. 



GENERAL COMMENT. 



Great care should be paid to the minute morphology / 

 of each organism, not only in the host-plant but also in 

 a variety of cultures, old and young, so that a body of 

 knowledge more exact than we now possess shall be grad- 

 ually accumulated for differential and systematic purposes. 

 Careful drawings and photographs should be made. The 

 Abbe camera is a great help in making drawings (fig. 121). 

 For such study the Zeiss apochromatic lenses and com- 

 pensating oculars can not be recommended too highly, 

 particularly the 16 mm., with the 12 and 18 compensating 

 oculars for studying the margins of colonies, and the 2 mm. 

 1.30 11. ap., with the 8 and 12 compensating oculars for the 

 more detailed study of the individual rods. The writer has 

 also made much use of the Zeiss 3 mm. 1.40 n. ap. apochro- 

 matic objective. The Zeiss screw, or filar, micrometer com- 

 bined with a No. 12 compensating ocular (fig. 23) will be 

 found very useful. For photographic purposes the projec- 

 tion oculars or the 4 or 6 compensating oculars may be used. 

 Robert Koch was entirely correct in saying : "A general 

 use of photography in microscopic works would certainly 

 have prevented a great number of unripe publications." 



Fig. I9.t 



*Fic. 18. Bacterium camfcstre. Cover-glass (smear) preparation from the vessels of a cab- 

 bage plant received from Racine, Wis., Sept. 19, 1896. Stained with carbol-fuchsin. Drawn from 

 a photomicrograph. X 1,000 circa. 



tFic. 19. Bacterium camfestre from an old culture on 23 per cent grape-sugar agar, showing 

 long filaments. Cover stained I hour and 20 minutes in gentian violet (i part saturated alcoholic 

 solution plus I part water). Many of the rods stained feebly. Tube inoculated June 30, 1898. 

 Cover prepared Aug. 8. Drawn directly from the slide. X 1,000. 



