142 SUMMARY OF CURRENT RESEARCHES RELATING TO 



In most cases in which an animal egg or embryo is encased in chitin, 

 the best results have been obtained by straining the sections after they 

 have been cut and fixed to the slide. If the specimen is small, staining 

 in toto — after having the chitin softened, or if before this has taken 

 place, after having made an entrance through the chitin with the point of 

 a needle — is equally good. The greatest difficulty, and practically the 

 only one which is met with, is that the Labarraque solution not only 

 attacks the chitin itself, but after a time the soft tissues of the animal — 

 apparently the connective tissue. Where the chitin surrounds the 

 object completely, as is the case with the cockroach's raft, the object 

 can be removed from the solution as soon as the chitin is softened, and 

 before the underlying parts have been attacked. In cases like this the 

 solvent is at its best. 



Very often, however, the soft tissues of the animal are exposed in 

 places between the chitin covering. This is well illustrated by the joints 

 of insects' legs, &c., and very frequently these exposed places are attacked 

 before the chitin is completely softened, thus causing the joints, if much 

 handled, to fall apart. By judiciously diluting the solution and taking 

 the parts to be softened from it before the joints are attacked, its appli- 

 cation will be found practicable even here. 



The greatest difficulty of all is when the chitin is internal, completely 

 surrounded by soft tissue. Better results are obtained here with very 

 dilute solutions — diluted from eight to ten times, or even more. It must 

 be admitted that in this last case the application of the solvent is more 

 doubtful, and of not nearly so much service as in the first and second 

 supposed cases. 



Strong solutions, then, had better be used only when the chitin 

 completely surrounds the soft animal parts, and dilute solutions must be 

 used in all cases where these latter substances are exposed. The solu- 

 tion not only softens the chitin, but removes all pigment either in the 

 chitin or in the tissue beneath, and this is at times advantageous. 



Bonda's Hardening Method.* — Dr. C. Bonda describes a new harden- 

 ing process especially adapted to the central nerve-system. It is briefly 

 as follows : — 



The material in mass (as for instance the brain of a large dog) is 

 placed for from twenty-four to forty-eight hours in a 10 per cent, 

 aqueous solution of pure nitric acid, whence it is removed without 

 rinsing into a solution of potassium bichromate, made by dissolving one 

 volume of a cold saturated solution of the salt in two volumes of water. 

 The bichromate solution must be replaced in the course of a few hours 

 with a solution consisting of equal volumes of the saturated solution and 

 water. In this the material is left until sufficiently liardened. It is 

 recommended that brain and spinal cord be kept at least eight days in 

 the fluid, and that the temperature be maintained at about that of incuba- 

 tion, or say from 100° to 110° F. The author highly eulogizes the 

 manner in which material thus hardened shows up after staining with 

 heematoxylin. 



* St. Louis Med. and Surg. Journ., Iv. (1888) p. 230, from Centralbl. Med. 

 Wise. 



