ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



645 



and between the two exists an association or symbiosis. The presence of 

 the bacterium is favourable to the development of the amoeba, as it forms 

 ammonia and thus maintains the alkalinity of the medium. On the other 

 hand the amceba supplies the bacterium with organic substances. Though 

 pure cultures of D. mucoroides can be obtained on gelatin and agar 

 media, yet their development is not nearly so good as when they are 

 accompanied by their customary followers. 



Perfectly pure cultures are weak, easily perish, and produce mostly 

 dwarf forms. Pure cultures do not give at all a correct picture of the 

 normal growth of these organisms. 



(2) Preparing Objects. 



Demonstrating Bone Lacunae.* — • Dr. G. Schmore demonstrates 

 bone lacunaB and canaliculi by meaus of thionin and picric acid. 



The thionin solutions recommended are :— (1) a saturated solution in 

 50 per cent, alcohol 2 parts ; water 10 parts. (2) 1 per cent, carbol water 

 90 parts ; saturated solution of thionin in 50 per cent, alcohol 10 parts. 



After staining with thionin for 5-10 minutes the sections are 

 washed and then immersed in saturated aqueous solution of picric acid 

 for a half to one minute. Excess of stain is removed in 70 per cent, 

 alcohol. The sections are mounted in balsam. 



Fig. 17S. 



(3) .Cutting-, including- Imbedding- and Microtomes. 



Microtome with Arc-movement of Knife for Section-cutting under 

 Water, Alcohol, &c.j — Hcrr Paul Thate, of Berlin, describes a form 



* Oentralbl. f. allgeoi. Pathol, u. pathol. Anat., x. (1899) pp. 745-9. 

 t Zeit. f. angew. Mikr., June 1900, pp. 73-6 (2 figs.). 



