156 E. Nunn. On the Development of [June 15,. 



animals, while the same fluids unheated, are invariably and fatally 

 infective in infinitely smaller quantities. 



In Davaine's septichaBmia in the rabbit, I have found throughout 

 these experiments that the period of incubation is remarkably constant, 

 death, after the first generation of infection by putrid blood, almost 

 invariably occurring from about twenty to twenty-five hours, and con- 

 sequently that if it does not occur within about that period, it may be 

 concluded that infection has failed ; it may die subsequently, as rabbits 

 in confinement constantly do, more especially under the conditions in 

 which they are kept in laboratories ; but unless within about the 

 period specified they do not die infected with specific septichsemia, 

 the characteristic organisms are not found in the blood, nor is that 

 blood infective ; hence it is not necessary to observe such animals for 

 more than a few days after inoculation. 



These experiments were conducted in the laboratory at University 

 College, with the co-operation of Dr. Burdon Sanderson, and at his 

 suggestion. 



XVII. " On the Development of the Enamel of the Teeth of Ver- 

 tebrates." By Emily Nunn. Communicated by Professor 

 Huxley, F.R.S. Received June 14, 1882. 



[Plates 2-4.] 



The question of the origin of the enamel of the teeth in vertebrate 

 animals has been the subject of much discussion. It has been held — 

 1st, that the enamel results from the calcification of the enamel cells 

 (Tomes, Waldeyer, Edwards) ; 2nd, that it is formed by excretion 

 from those cells (Kolliker, Hertwig, Ley dig) ; and, 3rd, that it is not 

 formed by these cells at all, but has the same origin as the dentine, 

 whatever that may be.* 



Again, there are numerous opinions concerning the nature and origin 

 of the cuticula dentis : — 1, that the cuticula is the persistent basement 

 membrane itself (Huxley, Hertwig, Leydig) ; 2, that it is the altered 

 enamel membrane ; 3, that it is the external layer of cells of the 

 enamel organ (Waldeyer) ; 4, that it is the metamorphosed stratum 

 intermedium of the enamel organ (Lowve) ; 5, that it is the ends 

 (Becheln) of the cells of the enamel membrane (Kollman) ; 6, that it 

 is a dermic structure (Tomes) ; 7, that it is an excretion of the cells of 

 the enamel membrane (Kolliker). 



* Huxley, " Tegumentary Organs," " Encyclopedia of Anat. and Phys.," vol. v,, 

 Sup., gives reasons for considering the whole tooth ecderonic, but adds, " All these= 

 points can only be decided by a much more extensive series of investigations." 



