No. IT.] APPENDIX. 145 



become black by being macerated too long. It is also to be observed 

 that the parts of animals preserved in the fossil state are those which 

 longest resist putrefaction. It having been likewise shown that the degree 

 of change does not depend upon the age of the bed in which the fossil 

 occurs, it is a curious subject of inquiry for the geologist to ascertain how 

 far the conditions necessary to putrefactive air, a certain temperature and 

 moisture, were present in those strata in which the change has been great; 

 how far they were absent in those in which the change has been small. 



No. II. 



ON THE CHEMICAL NATURE OF THE EXTERNAL ENVELOPE 

 OF THE FROG'S SPAWN. By ALFRED SMEE, Student of King's 

 College. (' London Medical Gazette/ May 26, 1838.) 



THE nature of the envelope of the spawn of the frog does not seem to 

 have been investigated chemically, some authors stating generally that 

 it is of an albuminous, others that it is of a gelatinous nature. To me, 

 however, it appears to be neither of the above substances, but rather a 

 form of mucus, as the following observations show : 



1. When the envelope is separated from the ova, it gradually sinks 

 in water. 



2. It is not soluble either in hot or cold water, but swells considerably 

 when first placed in it, after which it may be dried without losing any of 

 its former properties, for on the addition of water it will again swell to its 

 former size and appearance.* 



3. When portions of the external covering were boiled in water, it was 

 not dissolved, nor was there any coagulation. 



4. When the spawn was treated with nitric acid, there was no coa- 

 gulation, but after a short period the external covering was dissolved, 

 leaving the ova. 



5. Sulphuric acid had the same action on the spawn as the nitric. 



6. Muriatic acid, like the preceding acids, did not coagulate, but 

 dissolved the envelope. 



7. Acetic acid, even when pretty strong, produced little or no effect 

 on the spawn. 



8. The action of the oxalic acid was found to be the same as the 

 acetic acid. 



9. The envelope was then treated with a solution of caustic potash, 

 when it was dissolved. 



10. Ammonia produced apparently no effect on the envelope. 



11. When the ova were treated with alcohol, no coagulation ensued, 

 nor was the envelope dissolved. 



12. Tincture of galls was also found to produce no effect on the 

 envelope. 



* It does not appear, after a long time, to be dissolved, as after five or six 

 weeks ; but probably here decomposition may, in some manner, alter its nature. 



L 



