258 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Different Methods of Staining Tubercle Bacilli.* — Karl Bergen 

 gives a critical review of the literature of this subject, describing the 

 staining methods employed by various authorities, and dwelling particu- 

 larly upon the granules (sc. spores) which are brought out by some 

 methods. For his own research, he selected Much's modification of 

 Gram, Ziehl-Neelsen, and Gasis' methods as the three most promising. 

 Gasis' plan is a reversal of the Ziehl-Neelsen procedure. After staining 

 in an acid stain, the film is decolorised by alkali. Gasis maintained 

 that the alkali-fast property of tubercle bacilli is possessed by organisms 

 in very young and very old cultures, organisms not often acid-fast, as 

 well as by bacilli of the average period. 



Bergen found that the advantage of the Ziehl-Neelsen method lay in 

 its ease and certainty. On the other hand, the granular form of the 

 tubercle bacillus was hardly stained at all, and some young forms did not 

 retain the stain. Modified Gram staining is not suitable for differential 

 diagnosis, and in preparations from pure cultures a clear picture is not 

 obtained. The method of Gasis is peculiarly suitable for investigation 

 of minute structure. It gives beautiful films. On the other hand, the 

 technique is difficult, and the results therefore may be inconclusive in 

 cases of differential diagnosis. This method is perhaps the most suitable 

 for making permanent preparations. 



Further, Bergen gives an interesting account of the effects obtained 

 by him as a result of combinations of these methods. 



Studying the Development of Dentine in Mammalia.f — For the 

 histological investigations in this research, G. Heinrich used a variety 

 of reagents such as formalin, alcohol, Zenker's fluid, osmic acid, and 

 others for fixing his material. Formalin gave the best results, especially 

 when used in connection with the silver-staining process. 



By staining sections successively with iron-alum-haBmatoxylin, dilute 

 rubin S and Heidenhain's connective-tissue stain, good contrasts were 

 obtained. Connective-tissue fibres and the uncalcified ground substance 

 were stained deep red, calcified areas black, and tooth-fibres pale grey. 

 The odontoblasts are stained more deeply than the connective-tissue 

 cells. 



In the silver process, the paraffin sections, after prolonged soak- 

 ing in 2 p.c. silver nitrate, are treated with an ammoniacal silver 

 solution. The stain is developed in a formalin bath, and treatment with 

 gold chloride, followed by hyposulphite, completes the silver staining. 

 The sections are then mounted on slides and washed with xylol to remove 

 paraffin, and then with alcohol. Alcoholic solution of light-green is 

 used as counterstain, and the section is then dehydrated and mounted in 

 Canada balsam. These preparations are well adapted for microphoto- 

 graphic purposes. 



(6> Miscellaneous. 



Experimental Study of Development during the past decade. f 

 The advances in this branch of investigation are surveyed by 0. Levy. 



* Centralbl. Bakt., lte Abt., liii. (1910) pp. 174-208. 



t Arch. Mikr. Anat., lxxiv. (1909) pp. 783-8. 



% Zeitschr. wiss. Mikrosk., xxvi. (1909) pp. 426-73. 



