372 CONNECTIVE TISSUES. 



The muco-periosteum is grasped with a pair of forceps and stripped 

 from the bone, when the tooth-germs will come away attached thereto. 



Sansom's modification of Carnoy's mixture, employed at blood- 

 heat, is particularly effective when the tooth-germs have been 

 exposed in the manner outlined above, fixation therein being com- 

 plete in from five to ten minutes. They are then passed through 

 successive baths of alcohol of 30 per cent, and 50 per cent., each for 

 fifteen minutes ; 70 per cent., to which is added tincture of iodine, 

 for four hours ; 90 per cent, for thirty minutes ; and into two changes 

 of absolute alcohol, each for fifteen minutes or longer. 



The tooth-germs are then transferred to a mixture of equal parts 

 of absolute alcohol and carbon disulphide for one hour, two changes 

 of pure carbon disulphide, each of fifteen minutes, then for thirty 

 minutes into carbon disulphide saturated with paraffin at 30 C., 

 transferred to carbon disulphide saturated with paraffin at 42 C. 

 for a like period, and finally into two baths of paraffin, in each 

 half an hour. Imbed for cutting in pure paraffin. 



By the employment of this method the amount of shrinkage in 

 the tissues is extremely slight and the dentine does not become 

 hardened, so that the tooth-germs of the incisors may be cut without 

 decalcification. In the case of the canine and molar tooth-germs 

 a short period of decalcification may be necessary, and for this 

 purpose a rapid and delicate method lies in the employment of 

 ZEIGLER'S method (Festschr. f. Kupffer, 1899, p. 51), in which, by 

 the use of a 5 per cent, solution of sulphurous acid, the insoluble 

 tricalcium phosphate is changed into the readily soluble mono- 

 calcium phosphate. 



To demonstrate cytological detail no stain equals iron-hsema- 

 toxylin followed by a counter-stain of picric-lichtgrun or of Rubin S 

 in picrate of ammonia. 



It cannot be too strongly emphasised that the precision of staining 

 methods depends on the rapidity ivitli ivhich fixation of the tissues is 

 effected after death. Refer to 31. 



For large jaws imbedding in celloidin, or, when serial sections are 

 required, double imbedding in celloidin, parlodion or photoxylin 

 and paraffin is recommended ( 171). 



MUMMERY (Phil. Trans. B., ccviii, 1917, p. 258) deprecates the 

 employment of paraffin for imbedding the tooth-germs of fishes, 

 considering the heat employed to be very injurious to the delicate 

 enamel organs, and advocates the use of the freezing method in 

 obtaining sections. See carbon disulphide method above. 



NEALEY (Amer. Mon. Mic. Journ., 1884, p. 142 ; Journ. Eoy. Mic. 



