122 



314 J. A. macwilliam 



It may be remarked that in neither of these explanations is it definitely 

 stated whether the whole of the venous system is regarded as depleted 

 or full — according to one view or the other — or whether the state of 

 a, the large venous trunks in the thorax and abdomen, or h, the veins 

 among or near the muscles in the trunk and limbs are specially in 

 question. Rapport (108) noted variations in the duration of the sec- 

 ondary rise after moderate and great efforts respectively. 



Observations by C. Reid (110) in this Laboratory show that the 

 rate, character and extent of the pressure changes after the end of the 

 exercise vary much in different individuals and in the same individual 

 under different conditions. 



The maximum height attained by the subsequent rise of pressure, 

 when such occurs, varies much and bears no precise or constant rela- 

 tion to the maximum height during the period of exertion, though 

 under some conditions it approximates or corresponds to that maximum. 



After a type of exercise where the raised pressure during the exercise 

 shows a simple decline afterwards, without a subsequent rise, the 

 rate of the decline varies considerably, and measurements taken at 

 some fixed point of time (e.g., | minute) are not to be relied on. Again, 

 in those forms of exercise where a subsequent rise does present itself, 

 occurring in varying degree after a preliminary fall, it is obvious that 

 much will depend on the exact point in the series of changes at which 

 the estimation is made. Measurements at half a minute after the 

 cessation of exertion will naturally give very different results according 

 as a subsequent rise develops or a simple progressive decline occurs; 

 even in the latter type the finding of equal readings at the half minute 

 interval in two different individuals or in the same individual at dif- 

 ferent times and under different conditions does not prove that the 

 maximum pressures attained during the exercise were equal in the two 

 instances. It is to be emphasised that measurements during the 

 period of exertion constitute the only valid evidence as to the actual 

 rise of pressure. It is not surprising that many discordant results 

 have been recorded by different observers dealing with exercises of 

 different types and duration or even with comparable exercises, when 

 the estimations are made after the end of the period of exertion. Quite 

 small rises (e.g., 16 mm.) have been reported after short spells of severe 

 exertion involving dyspnea with doubling of pulse rate, etc., when the 

 actual pressure during the exercise has really been greatly raised. 



Whatever significance may be attached to such estimations for some 

 purposes, it is clear that they are not reliable for determining the 



