602 SECTIONAL TRANSACTIONS.— I. 



depression of the percentage of fat will be of use in the study of lactation, it seems 

 certain that the richness of the diet in vitamin D is a factor which cannot be neglected. 



Dr. N. C. Wright. — One of the preceding contributions has dealt in general 

 terms with the calcium metabolism of lactating cows. In this paper the actual 

 reactions controlling calcium secretion in milk are discussed. 



The concentration of calcium in milk is more than ten times higher than that in 

 blood ; that is to say, the milk cells appear to have the property of selectively absorbing 

 this element from its very low concentration in blood plasma. Physico-chemical 

 investigations on artificial systems have pro\'ided evidence that two general reactions 

 exist which may cause this accumulation of calcium in milk : first, the action of the 

 casein, which is synthesised in the milk cells of the mammary gland from the freely 

 diffusible amino-acids of the blood (Gary) and is capable of causing a selective 

 absorption of calcium by the formation of the slightly dissociated calcium caseinate ; 

 and second, the process of supersaturation of this caseinate solution with calcium 

 phosphate, leading to the formation of a colloidal and non-diffusible solution of this 

 salt, which is consequently trapped in the mUk cells. Such supersaturation may be 

 expected as a result of (a) the free diffusion of calcium ions from the blood, ard (6) the 

 presence of high concentrations of phosphate ions due to the breakdown of the 

 phosphatide molecule in the formation of milk-fat (Meigs). 



Evidence that these two general reactions control calcium secretion is provided 

 from the three following facts : (1) previous work has already shown that the greater 

 part of the calcium in milk exists either as caseinate or as colloidal phosphate ; 

 (2) the calcium content of milk is very constant, a fact which we should expect if 

 calcium secretion is governed by a physico-chemical equilibrium in which the diffusible 

 blood calcium is itself constant ; and (3) the concentration of calcium in milk should 

 be influenced by just those factors which influence calcium deposition in bone (an 

 analogous process of supersaturation). Experiments with Vitamin D and ultra-violet 

 radiation support this fact. 



Mr. J. S. Fulton and Prof. B. A. McSwiney. — Pulse Velocity in Central 

 and Peripheral Arteries in Man. 



Measurements of pulse velocity have been made in the different arteries of man 

 by use of the hot wire sphygmograph. In the arm the pulse velocity of the brachial 

 artery is found to be lower than the pulse velocity of the radial artery, which indicates 

 that the extensibility of the brachial is greater than that of the radial artery. 



Mr. W. D. Paterson. — A New Type of Recording Oscillometer. 



In the course of an investigation into the rapid increase of blood pressure in man 

 during the onset of muscular exertion, it was considered desirable to obtain values for 

 diastolic in addition to systolic pressure in the brachial artery as frequently and 

 accurately as possible. Under such conditions the auscultatory method was found 

 to be almost impracticable, and none of the well-known instruments indicating or 

 recording air pressure oscillations in the pneumatic armlet proved adequate. 



Eventually a new type of recording oscillometer was designed, and this proved 

 capable of giving a large uninterrupted record of the series of oscillations due to 

 arterial pulsations even during quite a rapid continuous fall in the average armlet 

 pressure. As the base line traced out is regular and horizontal, the rapid diminution 

 in size of oscillations immediately following a plateau of maximum range provides 

 an easily recognisable index of diastolic blood pressure, in close accordance with the 

 marked decrease in loudness of the sounds heard during auscultation. 



The instrument is so sensitive that respiratory variations in blood pressure are 

 clearly shown, but a mercury manometer, though in free communication with the 

 pressure chamber of the oscillometer, is immune from any fluctuations and so records 

 the average armlet pressure well. 



By employing a double overlapping armlet, a very sharp criterion of systolic 

 pressure can easily be obtained. This index, also sensitive to respiratory fluctuation 

 of pressure, consists in the initial definite appearance of oscillations after their com- 

 plete absence during higher armlet pressures. 



In this way systoUc and diastolic pressure indices and pulse rate can all be included 

 in a single ink trace and obtained every half-minute or so, even from a subject under- 

 taking moderately heavy work on a stationary ergometer. 



