1891.] On the Structure and Development of Dentine. 319 



As regards the principal effect, reduction of blood pressure, the 

 activity (extent of reduction) of the various nitrites takes the follow- 

 ing order when equal volumes are administered to animals by inha- 

 lation : (1) secondary propyl ; (2) tertiary butyl ; (3) secondary 

 butyl, (4) isobutyl, nearly equal ; (5) tertiary amyl ; (6) -amyl, 

 (7) /3-amyl, nearly equal ; (8) methyl ; (9) butyl ; (10) ethyl ; 

 (11) propyl. 



The order is somewhat modified when the nitrites are given by 

 intra-vascular injection. When the duration of the sub-normal 

 pressure is considered, the order is nearly the reverse of that given 

 above, the effect of methyl nitrite being the last, and that of secondary 

 propyl nitrite one of the first, to disappear. In contrasting the 

 results of the measurement of pulse acceleration produced by these 

 nitrites, it is noticed that their activity in thia respect does not follow 

 the same order as that in reducing blood pressure, the amyl nitrites 

 in particular occupying a higher position in the table. The causes of 

 these differences will be considered in the second part of this paper, 

 in conjunction with a discussion of the relation of the chemical con- 

 stitution of the nitrites to the physiological effects now described, 

 and also to those produced in striated muscle, a description of which 

 will form part of the subsequent communication. 



In order that the physiological data might be placed on an abso- 

 lutely satisfactory basis for chemical discussion, we determined at the 

 commencement of last year to repeat all the more important physio- 

 logical experiments. This necessitated the labour of preparing fresh 

 specimens of the nitrites. The results of these confirmatory experi- 

 ments have been in every respect satisfactory, since they differed 

 in no important respect from those previously obtained. 



The chemical part of this enquiry has been conducted in the 

 Research Laboratory of the Pharmaceutical Society,, in London, 

 whilst the physiological experiments have been made in the Pharma- 



logical Laboratory of the University of Aberdeen.. 



Some Points in the Structure and Development of 

 Dentine." By J. HOWARD MUMMERY. Communicated by 

 0. S. TOMES, F.R.S. Received February 7, 189L 



(Abstract.) 



e purpose of the present paper is to show that there are appear- 

 s in dentine which suggest that it is formed by a connective 

 tissue calcification, and that the process is more closely analogous to 

 the formation of bone than has usually been supposed. 

 The varied theories held as to the structure and development of 



