764 SUMMARY OF CDBEENT RESEARCHES RELATING TO 



gelatin. The organ is, of course, placed in a water-bath during the 

 injection. When the operation is completed, the preparation is re- 

 moved and allowed to cool. It is now easy to insert a canula into the 

 liner vessels, which are distended by the injection-mass. When the 

 canula is fastened, the preparation is placed in warm water again. After 

 an immersion of a few minutes the gelatin is liquefied, and then the 

 inject ion -mass is easily syringed in. 



Demonstrating the Spermatogenesis of Hydra.* — E. B. Downing 

 used a variety of fixatives, including osmic-Merkel, Hermann's, 

 Perenyi's ehromacetic, Flemming's, Gilson's mercuro-nitric, Carnoy's 

 acetic-alcohol, Kleinenberg's picro-sulphuric, Graf's chromoxalic, varying 

 strengths of picro-acetic, and hot corrosive. The first three were the best, 

 the osmic-Merkel working especially well. A h p.c. solution of osmic 

 acid was used to kill the animals. The hydra was placed in a watch- 

 glass, in as small a drop of water as would allow the animal to 

 expand well. When expanded, about lOc.cm. of the osmic-acid solution 

 was poured over it, death mostly occurring without any contraction. 

 After about a minute the animal was transferred to Merkel for 24 hours. 

 It was then dehydrated in graded alcohols, cleared in xylol, and im- 

 bedded in paraffin. A variety of stains was used, the best being iron- 

 htematoxylin, Bordeaux red, orange G, and safranin-gentian-violet. 



The preparations were cleared with oil-of-bergamot or cedar-oil, and 

 the sections mounted in balsam or in thick cedar-oil. 



The best results were obtained from the osmic-Merkel or the Perenyi, 

 followed by iron-hasmatoxylin and Bordeaux-red, or for count of 

 chromomeres, by safranin. Gentian-violet was the best stain to dif- 

 ferentiate the gland-cells of the endoderm, and was used after iron- 

 hsmatoxylin. 



Decalcification of Dental Enamel.f — C. F. Bodecker remarks that 

 by the ordinary methods of decalcification, the protoplasmic constituent 

 of the enamel of teeth is torn off from the dentine and gets washed 

 away. This disaster is avoided by the following procedure : The pre- 

 parations pass through the usual processes until they come to thin 

 celloidin. From this they are transferred to the decalcifying solution, 

 which consists of thick celloidin solution, to which 6-10 p.c. strong 

 nitric acid has been added. The consistence of the solution must be 

 maintained by the occasional addition of ether and alcohol. 



The duration of the decalcifying process depends on the size of the 

 preparation — e. g. slices about 30 /* thick are ready within two weeks, 

 while those 1 mm. thick require about two months. 



After the preparation has lain in the acid solution for a couple of 

 days it assumes a chalky appearance, but as decalcification proceeds the 

 enamel becomes transparent, so that at last it is almost imperceptible. 



When this stage is reached, the celloidin is allowed to harden. 



On account of the difficulty of making thin celloidin sections, it is 

 advisable to imbed the block in paraffin. 



* Zool. Jahrb., xxi. (1905) pp. 370-426 (3 pis.). 



t Zeitschr. wiss. Mikrosk., xxii. (1905) pp. 190-2 (1 pi.). 



