MORPHOLOGY. 



23 



Involution Forms. 

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



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

 occur ? Are the}- living or dead ? Isolate in 

 hanging drops of bouillon and detennine whether 

 they are stages in development or only degenera- 

 tion forms. Are Y-shaped or branched fonns 

 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 many obsen-ers. (Consult 

 numerous citations in the Bibliography of General 

 Literature, X). The most recent paper is b)- Albert 

 Fig- 18* Maassen (Arb. a. d. Kais. Gesundh., Bd. XXI, H. 3, 



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 voung, so that a bod\- 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 n. ap., with the 8 and 12 compeusating oculars for the 

 more detailed study of the indi\-idual 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 \-er}- useful. For photographic purposes the projec- 

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

 Robert Koch was entireh' correct in saying : "A general 

 use of photography in microscopic works would certainly 

 have prevented a great number of unripe publications." 



*FiG. 18. — Baclcrium campcstrc. Cover-gia^s (snioar) .preparation from the vessels of a cab- 

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

 a photomicrogTaph. X 1,000 circa. 



fFiG, 19. — Bacterium campcsirc from an old cultnre on 23 per cent grape-sugar agar, showing 

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

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

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



