] 905 -6. ] Standardising Suprarenal Preparations. 163 
A similar curve of increased pressure was given when the same 
amount of adrenalin was injected towards the end of a fall of 
pressure from sodium nitrite (fig. 2), and during the slowly 
rising pressure produced by a weak solution of barium chloride 
('5 c.c. of *5 per cent, solution). 
This weak solution, then, *0000031 gram per kilo of body 
weight, produces a distinct effect when the blood pressure is 
normal, when it is falling gradually, and when it is being increased 
slowly. 
With a reliable adrenalin preparation available to give a 
standard of comparison, this method affords an excellent and 
easy means of standardising any preparation. But when this is 
not available the method is not so satisfactory. 
3. Antagonism to definite Doses of Vaso-dilators . — On account 
of the disadvantages of these methods, the plan of standardising 
against a vaso-dilator of known composition was tried. The 
marked peripheral vascular dilatation caused by the nitrites 
suggested their use. It is recognised that all the nitrites cause 
vascular dilatation, but their effects differ in degree and in dura- 
tion. The nitrate esters which act as nitrites were not available 
because of their insolubility. As Atkinson * points out, nitrous 
acid is too unstable to he used. The amyl base in amyl nitrite 
has a decided action of its own, and the alcohol required to 
keep it in solution increases the dilatation. Sodium has not a 
well-marked pharmacological activity, and so sodium nitrite is a 
convenient salt to use in order to get a nitrite effect. 
Hay f states that nitroglycerin is chemically a nitrate of glyceryl ; 
in an alkaline fluid such as the blood, it is decomposed and a 
nitrite is liberated. Marshall j does not agree with this view 
of the action of nitroglycerin. He contends that it probably 
remains unchanged and is not reduced until it reaches the 
tissue cells. Wherever the seat of the chemical change may 
be, there is no doubt that nitroglycerin acts physiologically as 
a nitrite. 
Sodium nitrite was first used in this series of experiments. 
* Journal of Anatomy and Physiology, vol, xxi. p. 225. 
f Practitioner, vol. xxx., 1883, p. 422. 
X Journal of Physiology, 1897-98, p. 1. 
