788 AKLIE V. BOCK 



suggested that the ability of man to withstand changes in his environ- 

 ment, such as extremes of heat and cold, is due to adjustments made by 

 the body fluid to meet the altered conditions. It is this facility to main- 

 tain optimum conditions for cellular activity, together with the regulation 

 of the total volume of body fluids that enables all higher forms of life to 

 exist in comfort within the environment. 



The cellular fluid has been spoken of as fixed, in comparison with the 

 blood, for example. There is, however, a constant interchange between 

 the cells and the tissue fluid which is of necessity a local interchange. 

 With the details of cellular activity the present discussion is not 

 concerned. 



With regard to lymphatic fluid, it need only be said that it repre- 

 sents tissue fluid collected into organized channels, to be returned to the 

 cardiovascular system in order to complete the major part of the cir- 

 culatory exchange of fluid in the tissues which began with the passage of 

 nutrient fluid from the capillary walls. 



The tissues everywhere throughout the body are bathed in fluid that 

 fills the tissue spaces. Since the metabolism of tissue cells is carried on 

 through the activity of 'this medium the tissue fluid, in a sense, becomes 

 the most important of the body fluids, as Starling suggests. This fluid 

 traverses the system of tissue spaces that form a rather complete circula- 

 tory system which, as Meltzer(fr) has shown, may be in part independent of 

 the cardiovascular system. When the normal quantity of tissue fluid is 

 greatly altered through defect in absorption, or in elimination of fluid, or 

 by direct loss of fluid, there are definite symptoms traceable to such a 

 disturbance. The importance of the tissue fluid which is the last vehicle 

 for the transport of nutrient material to the cell, and the first to receive " 

 the waste products of metabolism, cannot be too much emphasized. 



Of all the body fluids, the blood occupies the first place in the minds 

 of clinicians, and yet it is only one unit of the various fluid phases within 

 the body. It exerts, however, the controlling influence in the maintenance 

 of function in the normal organism. It is the main highway in the body 

 for distribution and elimination. Of its many characteristics we are 

 here concerned mainly with the question of the volume of the blood. This 

 is roughly one-eighth of the total fluid in the body, and has been found in 

 the normal individual to be a surprisingly constant quantity, subject 

 only to minor variations. Even in disease the variation from the normal 

 quantity is not often great. When the body is confronted with a loss of 

 fluid, such as may occur in severe diarrhea, fluid is withdrawn from the 

 tissue fluid to the blood. This is done in an effort to maintain nutrition 

 of the higher centers at the expense of the tissues in general. Thus, 

 individual cells may begin to suffer from failure of nutrition long before 

 the blood itself shows much evidence of depletion of fluid. This mech- 

 anism needs to be appreciated, since conditions in which actual concen- 





