63 



sodium carbonate solution in an incubator at 38 C. until examination 

 under the microscope shows that the cells have become disintegrated 

 and digested. The digestion fluid should be changed every day or 

 2 or 3 days. A varying length of time is necessary, sometimes a 

 month or more. Paraffin sections may also be submitted to digestion, 

 with or without the removal of the paraffin. 



The following method is recommended for the further preparation 

 of digested tissue. After washing thoroughly in running water to 

 remove the digestion fluid, the tissue is carefully imbedded in celloidin 

 ( 61 ) and sectioned, the sections being 20 to 30^ thick. These 

 sections are not fastened to the slide, but after having been brought 

 into 95% alcohol are placed in a concentrated solution of acid fuchsin 

 in 95% alcohol to which a drop or two (per 50 c. c.) of glacial acetic acid 

 has been added. After several minutes, the sections are rinsed in 

 95% alcohol to remove the excess stain, cleared in carbol-xylene and 

 mounted in balsam. By this method the delicate morphology is 

 preserved and a sharp stain is secured. 



The method of artificial digestion with trypsin or pepsin has 

 other applications in the histological analysis and it possesses a dis- 

 tinct value. 



CALCIFIED STRUCTURES BONE AND TEETH. 



(A) . Decalcification . 



184. For the purpose of investigating the soft structures of 

 tissues containing lime salts, such as bone, teeth, and calcified carti- 

 lage, it is necessary to remove the lime salts before sections can be 

 prepared in the usual way by a process known as decalcification. 

 Solutions of a large number of acids, combined or uncombined with 

 other substances, may be used as decalcifiers. Very satisfactory 

 are: (1) Hydrochloric acid, 1 c. c., 67% alcohol, 100 c. c. 



(2) nitric acid, 3 c. c.; 70% (67%) alcohol, 97 c. c., and 



(3) nitric acid, 5 c. c.; saturated aqueous solution of (potash) 

 alum, 50 c. c.; water, 50 c. c. 



In the first and second formulas the alcohol, in the third the 

 alum acts as a restrainer of the acid. The first or second of these 

 formulas is, perhaps, better for bone; the second has a more rapid 

 action and is possibly a better decalcifier for teeth. It is better to 

 let the decalcification proceed slowly for a longer time in an abundance 

 of fluid changed often, in order that the carbon dioxid may not be 



