BLOOD, RESPIRATION, CIRCULATION AND DISTURBANCES 303 



a precipitation takes place immediately, the precipitate consisting of a 

 mixture of calcium carbonate and phosphate. It is only because of 

 the presence of the serum colloids that this precipitation does not 

 occur. Accordingly, the serum colloids serve the purpose of keeping 

 soluble substances in solution and of releasing them at the proper 

 time. This phenomenon is of great physiological importance in the 

 formation of bone (see p. 268), and it is of great pathological signifi- 

 cance in gouty deposits (see p. 274). 



The surface tension of serum has been frequently studied in recent 

 years. The incentive was afforded by the observation of M. ASCOLI 

 and G. IZAR that the surface tension of immune serum was depressed 

 when it was united with its specific antigen (see meiostagmin reaction). 

 MORGAN and WOODWARD recorded especially exact determinations. 

 They found that the surface tension of healthy men did not vary 

 much, on the average (from 44.3 to 46.4), but that the diet might 

 cause marked variation. The surface tension is especially high in 

 some patients, especially nephritics (reaching to 51.4). Mammalian 

 serum does not differ much from human serum. 



Lymph. 



We can think of the lymph as a filtrate derived from the blood. 

 It does not by any means have a composition identical with blood 

 plasma; on the contrary, we find in it many metabolic products which 

 have entered it by diffusion from the cells it bathes. It is generally 

 assumed that the blood pressure affords the increased pressure 

 necessary for filtration; but I wish to call attention to the fact that it 

 may possibly be the pulsation which is of prime importance in this 

 instance, just as I have established for the glomerular filtration in 

 the kidney (p. 332). 



The Blood Corpuscles. 



The red blood corpuscles or erythrocytes present under the mi- 

 croscope the well-known round or elliptical shape with a thickened 

 rim, like a biconcave circular or elliptical plate. In reality, according 

 to the investigations of F. WEIDENREICH, they seem to approach 

 the shape of a spinning top (a cone with a convex base) ; so that under 

 the microscope their appearance is distorted. When they leave 

 the blood vessels we frequently encounter erythrocytes in rouleau. 

 SCHWYZER attributes this to the fact that the normal OH charge is 

 disturbed by the glass slide. In the blood vessels, however, the simi- 

 lar and equal charge of the vessel wall opposes the corpuscles and they 

 never form rouleau. In view of what follows, we should recall that 

 on swelling, they swell up symmetrically and have the shape of a pea, 



